Category Archives: Longevity

Physical Activity: Whence Its Healthfulness?

Posted by on October 11, 2012 101 comments

In our last post, Exercise: Is Less Better Than More?, I quoted four studies showing that light aerobic exercise, of the intensity of jogging at 10 or 11 minutes per mile, improved health up to a volume of about 30 minutes per day, but then the health benefits plateau. Light aerobic exercise seems to become unhealthy as the volume exceeds 50 minutes per day.

Today I’ll continue looking at low-level activity to try to clarify where the health benefits come from, so that we can better design a health-maximizing exercise program.

Sitting versus Standing

There seem to be negative health effects from even short periods – a few hours – of inactivity: sitting or lying down.

A recent systematic review, first-authored by TJ Saunders of Obesity Panacea, found that a single day of bed rest is sufficient to raise triglycerides, and that 2 hours of sitting increases insulin resistance and impairs glucose tolerance – moving the body closer to a diabetic phenotype. [1]

Research by Marc Hamilton found that sitting shuts down expression of lipoprotein lipase (LPL) in skeletal muscle, preventing muscle cells from importing fat. [2] A Science Daily article shows an interesting video based on this research. Here are blood samples after consumption of an identical meal eaten the same person; the left sample was taken after a meal eaten sitting down, the right sample after a meal eaten standing:

When sitting, dietary fats are taken up only by adipose tissue. When standing, they are taken up by muscle and adipose tissue both.

Time spent standing did more to push fat into muscle cells than vigorous daily exercise. This is significant because pushing nutrients into muscle cells promotes muscle growth. If you have trouble gaining muscle, maybe the problem is too much sitting, and what you need is not more intense workouts, but more frequent standing!

Sleep Is Good

Not all inactivity is bad, however. Sleep is highly beneficial.

Consequences of poor quality or insufficient sleep include:

  • Higher rates of cancer. [3]
  • Impaired immunity and vulnerability to infection. [4]
  • Higher rates of heart disease. [5]
  • Higher all-cause mortality. [6]
  • Faster cognitive decline with age. [7]
  • Shortening of telomeres. [8]
  • Higher rates of diabetes. [9]

One way to interpret this: Inactivity during the day is unequivocally bad, but inactivity at night may be a good thing.

This may be an indication that the benefits of activity come not through fitness, but through entrainment of circadian rhythms. To enhance circadian rhythms, we want daytime activity but night-time rest.

Activity at Work

If activity and exercise at work are good, it might seem a good thing to have an active job. Why not get paid for getting your exercise?

However, the data is not so clear. In comparisons of sedentary work with active work, usually the sedentary workers come out pretty well. For example:

  • In women, no relationship was found between occupational physical activity and heart disease risk. [10]
  • In the HUNT 2 study, people with metabolic syndrome were more likely to die of cardiovascular disease if their work included physical activity than if it was sedentary. [11]
  • In the Copenhagen City Heart Study, high occupational physical activity was associated with higher all-cause mortality. [12]

It seems that when it comes to routine physical activity, more is not better. Exercise is a stressor, and it’s easy to get too much. Being active for eight hours a day is too much.

How Much Activity is Optimal?

If we can easily get too much low-level activity, then what is the optimal amount?

I suggested in my last post that we don’t have an innate “activity reward” system in the brain because our hunter-gatherer ancestors got more exercise than they needed. If that’s true, then we can look to hunter-gatherers to see what constitutes enough activity.

So how much activity did hunter-gatherers get?

It’s been estimated that hunter-gatherers typically walk 5 miles a day, run 1 mile a day, and do various resistance-style carrying and lifting activities. For instance, anthropologist Kim Hill states:

The Ache hunted every day of the year if it didn’t rain. Recent GPS data I collected with them suggests that about 10 km (kilometers) per day is probably closer to their average distance covered during search. They might cover another 1-2 km per day in very rapid pursuit. Sometimes pursuits can be extremely strenuous and last more than an hour. Ache hunters often take an easy day after any particularly difficult day, and rainfall forces them to take a day or two a week with only an hour or two of exercise. Basically they do moderate days most of the time, and sometimes really hard days usually followed by a very easy day. The difficulty of the terrain is really what killed me (ducking under low branches and vines about once every 20 seconds all day long, and climbing over fallen trees, moving through tangled thorns etc.)

The Hiwi on the other hand only hunted about 2-3 days a week and often told me they wouldn’t go out on a particular day because they were “tired”. They would stay home and work on tools etc. Their travel was not as strenuous as among the Ache (they often canoed to the hunt site), and their pursuits were usually shorter. When I hunted with Machiguenga, Yora, Yanomamo Indians in the 1980s, my days were much, much easier than with the Ache. And virtually all these groups take an easy day after a particularly difficult one. [13]

So the Ache walked about 6 miles per day, ran about 1 mile; other groups did less, but all of them traversed more difficult terrain than modern walkers and runners. So it seems that 5 miles of walking and 1 mile of running per day on easy terrain might be a reasonable estimate for the optimal daily activity level.

Five miles is about 10,000 steps. A review of the evidence suggested that 7,000 to 11,000 steps per day achieves all the health benefits of walking. [14]

In a comment, Jason gave us a link to a Runner’s World article that contained figures from a recent paper [15]. These illustrate the plateauing of health benefits at a relatively low level of activity:

Above about 30 MET-hours per week of activity, corresponding to 2 hours per week (20 minutes per day) of running at 7 minutes per mile or 4 hours per week (40 minutes per day) of jogging at 10 minutes per mile, there are no health benefits to additional activity.

In other words, the benefits of exercise run out after running 3 miles or jogging 4 miles per day – not far from the hunter-gatherer activity level.

The shape of this curve is supportive of the idea that circadian rhythm enhancement, not fitness, is the cause of the health benefits of exercise. Levels of activity beyond running 20 minutes per day do increase fitness – every cross country or track team in the country trains at a higher level than this – but do not improve health; so health does not depend on fitness. It looks like we need a certain amount of activity to properly entrain our circadian rhythms – to tell our bodies that it is daytime, the time of activity – but once we’ve achieved that, we don’t need to do more.

Centenarians Don’t Over-Exercise

Dan Buettner, author of The Blue Zones: Lessons for Living Longer From the People Who’ve Lived the Longest, has said, “None of the longest-lived societies we studied exercise as we think of it.”

And, based on my readings of centenarian obituaries, it seems true that the longest-lived often don’t do a lot of exercise. A reader who has commented as “B.C.” emailed me a link to a New York Times story on Julia Koo, a centenarian who recently celebrated her 107th birthday in good health. Her secret to a long life: “No exercise, eat as much butter as you like and never look backwards.” [16]

Conclusion

It looks like if we want optimal health, at least four factors should influence our daily activity:

–          When it comes to vigorous activites like running, jogging, or lifting, we should do neither too much nor too little. A half hour of such activity per day may be optimal for health, an hour or more may do us more harm than good. Thus, occupations that require physical activity throughout the day may be health impairing.

–          Several hours per day of walking is probably beneficial.

–          The rest of the day should be restful, but not completely inactive. We should not go more than 20 minutes without standing.

–          There are reasons to believe that the benefits of activity may derive more from circadian rhythm entrainment than from fitness. If this is true, then it may be important to develop a routine that includes some activity every day, than it is to optimize fitness by a well designed high-intensity interval training and on-day/off-day protocol.

It really didn’t occur to me until we worked on the new edition of the book that circadian rhythms might be the reason for the health benefits of exercise. (We have more evidence in the book for this idea, including the observations that exercise in the day improves sleep quality at night, and that circadian rhythm disruption has similar health effects to sedentary living.) Since working through this research, I’ve become much more committed to doing something every day – but much less concerned about whether that activity is well designed to make me fit.

References

[1] Saunders TJ et al. Acute sedentary behaviour and markers of cardiometabolic risk: a systematic review of intervention studies. J Nutr Metab. 2012; 2012:712435. http://pmid.us/22754695.

[2] Hamilton MT et al. Role of low energy expenditure and sitting in obesity, metabolic syndrome, type 2 diabetes, and cardiovascular disease. Diabetes. 2007 Nov;56(11):2655-67. http://pmid.us/17827399.

[3] Nieto FJ et al. Sleep-disordered breathing and cancer mortality: results from the Wisconsin Sleep Cohort Study. Am J Respir Crit Care Med. 2012 Jul 15;186(2):190-4. http://pmid.us/22610391.

[4] Bollinger T et al. Sleep, immunity, and circadian clocks: a mechanistic model. Gerontology. 2010;56(6):574-80. http://pmid.us/20130392.

[5] Hoevenaar-Blom MP et al. Sleep duration and sleep quality in relation to 12-year cardiovascular disease incidence: the MORGEN study. Sleep. 2011 Nov 1;34(11):1487-92. http://pmid.us/22043119.

[6] Cappuccio FP et al. Sleep duration and all-cause mortality: a systematic review and meta-analysis of prospective studies. Sleep. 2010 May;33(5):585-92. http://pmid.us/20469800.

[7] Altena E et al. Do sleep complaints contribute to age-related cognitive decline? Prog Brain Res. 2010;185:181-205. http://pmid.us/2107524.

[8] Barceló A et al. Telomere shortening in sleep apnea syndrome. Respir Med. 2010 Aug;104(8):1225-9. http://pmid.us/20430605.

[9] Botros N et al. Obstructive sleep apnea as a risk factor for type 2 diabetes. Am J Med. 2009 Dec;122(12):1122-7. http://pmid.us/19958890.

[10] Mozumdar A et al. Occupational physical activity and risk of coronary heart disease among active and non-active working-women of North Dakota: a Go Red North Dakota Study. Anthropol Anz. 2012;69(2):201-19. http://pmid.us/22606914.

[11] Moe B et al. Occupational physical activity, metabolic syndrome and risk of death from all causes and cardiovascular disease in the HUNT 2 cohort study. Occup Environ Med. 2012 Sep 28. [Epub ahead of print] http://pmid.us/23022656.

[12] Holtermann A et al. Occupational and leisure time physical activity: risk of all-cause mortality and myocardial infarction in the Copenhagen City Heart Study. A prospective cohort study. BMJ Open. 2012 Feb 13;2(1):e000556. http://pmid.us/22331387.

[13] O’Keefe JH et al. Exercise like a hunter-gatherer: a prescription for organic physical fitness. Prog Cardiovasc Dis. 2011 May-Jun;53(6):471-9. http://pmid.us/21545934.

[14] Tudor-Locke C et al. How many steps/day are enough? For older adults and special populations. Int J Behav Nutr Phys Act. 2011 Jul 28;8:80. http://pmid.us/21798044.

[15] Chomistek AK et al. Vigorous-intensity leisure-time physical activity and risk of major chronic disease in men. Med Sci Sports Exerc. 2012 Oct;44(10):1898-905. http://pmid.us/22543741.

[16] James Barron, “Lessons of 107 Birthdays: Don’t Exercise, Avoid Medicine and Never Look Back,” The New York Times, September 24, 2012, http://cityroom.blogs.nytimes.com/2012/09/24/lessons-of-107-birthdays-dont-exercise-avoid-medicine-and-never-look-back/.

Exercise: Is Less Better Than More?

Posted by on September 22, 2012 60 comments

NOTE: Shou-Ching and I will be traveling in Europe next week; she’ll be speaking at this meeting and we’ll take a few days vacation. Blogging will resume on October 2 or so.

A New York Times column, “For Weight Loss, Less Exercise May Be More,” got some attention this week. It was based on a recent study of the effects of exercise on weight loss.

The Danish study [1] found that exercise is helpful for weight loss – but only the first 30 minutes of light exercise per day. Additional exercise had no effect on body weight – in fact it even seemed to diminish weight loss. Those who jogged for 60 minutes a day lost five pounds, those who jogged for 30 minutes lost seven.

The subjects wore activity tracking devices – Actigraph GT1-M devices, which are an older model of these and similar to a Fitbit – which produced a surprising result. Those who exercised 30 minutes a day were seemingly energized by their exercise, as they became more active in their daily lives – more likely to take the stairs, for instance. Those who exercised 60 minutes a day, on the other hand, seemed to be worn down by their exercise, and became less active in daily life.

It seems that 30 minutes of exercise improved health but 60 minutes of exercise may have diminished well-being. When it comes to exercise, perhaps, less is more.

A Well-Supported Result

While the Danish study [1] was novel in looking at how weight loss and non-exercise activity respond to exercise, it is not the first study to show that light activity may be healthier than intense activity.

In the new Scribner edition of our book, we greatly expand the part which discusses how to optimize immunity and heal or prevent disease. The new edition discusses exercise. We found a number of recent studies showing that light daily activity is as good or better than intense activity for health:

  • A study of American runners found that those who ran between 1 and 20 miles per week at a jogger’s pace of 10 or 11 minutes per mile reduced their risk of dying as much as those who ran more than 20 miles a week or who ran faster. [2]
  • Another Danish study reported that Danes who exercised two or three times per week for a total of one to two and a half hours reduced mortality by 44% and extended their lifespans by 6.2 years for men and 5.6 years for women. Those who exercised either more or less had less benefit. [3]
  • A study of 416,175 Taiwanese adults found that an hour and a half of moderate exercise per week (13 minutes per day) reduced mortality by 14% and extended lifespan by 3 years. An additional 15 minutes per day reduced mortality by only another 4%. Benefits peaked at 50 minutes of exercise per day. [4]

These are intriguing results. What’s more intriguing is that it doesn’t seem to matter how fit the exerciser is. People gain substantial health benefits from light exercise, even if the activity never makes them fit.

An Evolutionary Argument for Not Over-Exercising

Thanks to Stephan Guyenet, we’ve been talking a lot about the reward system of the human brain. It evolved in order to make us want to do healthy things, like braving the stings of angry bees to get honey from hives concealed high in trees.

David recently linked to an interesting post suggesting that our Paleolithic ancestors may have done a lot of honey gathering, which reminds me of this movie about the Hadza and their honey seeking:

Why did we develop an attractive taste for sugar, and why does the brain reward us for carb consumption? Presumably because the Paleolithic diet was too low in carbs for optimal health, and evolution wanted to encourage Paleolithic hunter-gatherers to gather more honey.

But, however valuable carbs are, it’s not clear that they are as valuable as the extra six years of life we obtain from light daily exercise. Yet there’s no innate reward for exercise. Many people are quite content to live their whole lives as couch potatoes.

Why didn’t evolution reward exercise, if it is as valuable as carbs? Probably because Paleolithic humans almost invariably got more exercise than they needed. Perhaps our brain evolved to prevent our ancestors from over-exercising, and now our brain unfortunately rewards us for over-resting!

Conclusion

It looks like exercise is healthful, but most or all of the benefits come from a relatively small amount – the first 30 minutes per day.

Doing the research for the new edition of our book has led me to revise my ideas of why exercise is beneficial, and how we should exercise to optimize health. In my next post, I’ll discuss why I think light exercise is most healthful, the tension between healthfulness and fitness, what I think a health-oriented exercise program should look like, and how my personal exercise activity has changed.

References

[1] Rosenkilde M et al. Body fat loss and compensatory mechanisms in response to different doses of aerobic exercise–a randomized controlled trial in overweight sedentary males. Am J Physiol Regul Integr Comp Physiol. 2012 Sep;303(6):R571-9. http://pmid.us/22855277.

[2] Gretchen Reynolds, “Moderation as the Sweet Spot for Exercise,” New York Times, June 6, 2012, http://well.blogs.nytimes.com/2012/06/06/moderation-as-the-sweet-spot-for-exercise/.

[3] European Society of Cardiology (ESC) (2012, May 3). Regular jogging shows dramatic increase in life expectancy. ScienceDaily. http://www.sciencedaily.com/releases/2012/05/120503104327.htm.

[4] Wen CP et al.  Minimum amount of physical activity for reduced mortality and extended life expectancy: a prospective cohort study. Lancet. 2011 Oct 1;378(9798):1244-53. http://pmid.us/21846575.

Do the Elderly Need Paleo More than the Young?

Posted by on September 15, 2012 47 comments

I also do work in economics and one of my favorite economics blogs is Evolving Economics by Jason Collins. He has an interest in biology and Paleo diets and recently linked to an interesting train of thought from evolutionary biologist Michael Rose.

Here is a summary from Peter Turchin, who adopted a Paleo diet this spring after talking to Rose:

We think of people having ‘traits,’ but actually we change quite dramatically as we age. … As an extreme example, consider reproductive ability, something of great interest to evolution. Humans do not reproduce until they reach a fairly advanced age of maturation (puberty). Young adults are not very good mothers or fathers, but they improve with age during their twenties. After that reproductive ability declines and eventually disappears. …

Ability to digest certain foods can also be age-dependent. I have already mentioned the ability to digest lactose, the sugar present in milk. Before we domesticated animals such as cows and sheep, only very young humans had this ability. Natural selection turned this ability off in adults because they never needed it (and it would be wasteful to continue producing the enzyme lactase that aids in the digestion of milk sugar). …

Because abilities to do something at the age of 10, 30, 50, etc. are separate (even if correlated) traits, they evolve relatively independently of each other. When grains became a large part of the diet, the ability of children to digest them (and detoxify the chemical compounds plants put into seeds to protect them against predators such as us) became critical. If you don’t have genes to help you deal with this new diet, you don’t survive to adulthood and don’t leave descendants. In other words, evolution worked very hard to adapt the young to the new diet. On the other hand, the intensity of selection on the old (e.g., 55 years old) was much less – in large part, because most people did not live to the age of 55 until very recently. …

The striking conclusion from this argument is that older people, even those coming from populations that have practiced agriculture for millennia, may suffer adverse health effects from the agricultural diet, despite having no problems when they were younger.

This is an intriguing argument. Several aspects of it are well supported: there has been recent evolution to enable people to cope with toxic diets, and there are substantial changes in how we respond to food as we age.

Recent Genetic Evolution

We know that there has been recent evolution for greater tolerance to evolutionarily novel foods such as wheat. This is (presumably) why peoples with a long history of grain agriculture are less obese and diabetic on “western” diets than people with a long history of eating healthy foods.

The Pacific islanders are a great example. The world’s highest obesity rates are in the Pacific – for instance, in the Kosrae district of Micronesia, 88% of adults are overweight and 59% obese – yet they were notably slim sixty years ago when still eating their traditional diets. [1]

In our book, we note that the traditional diets of Pacific Islanders are almost toxin-free. A logical inference is that because they have for millennia eaten the world’s least toxic diets, Pacific Islanders never needed to evolve (or lost) an ability to cope with toxin-rich diets, and now suffer much more harm from toxic foods than do peoples whose ancestors have eaten toxic diets.

Age-Based Differences in the Biological Response to Unhealthy Food

It’s also the case that we respond to food differently as we age.

It’s not only digestion, such as the age-related decline in lactase enzyme expression, that changes. There are metabolic changes.

The elderly consume far fewer calories than the young; presumably evolution selected for minimal food utilization so that they would not be a burden to those who had to hunt and gather on their behalf. Their contribution was likely cultural, which didn’t require extensive physical activity.

Another change is that the elderly become less likely than the young to store calories in adipose tissue. This has significant consequences.

We know from a broad range of evidence that adipose tissue protects other tissues from damage by lipotoxicity; and that when adipose tissue refuses to store fat, obesogenic diets lead to metabolic syndrome and diabetes. [2] So reduced storage of calories in adipose tissue in the elderly will lead to (a) reduced rates of obesity (as measured by adipose tissue accumulation), but (b) higher rates of metabolic syndrome and diabetes.

This is exactly what we see. Here are obesity rates by age group [3]:

Obesity rates for people over age 65 are lower than for people aged 30-64.

Here are diabetes rates by age group [4]:

Despite their lower obesity rates, the elderly have higher diabetes incidence.

This difference alone is sufficient to answer the question in our title: Yes, the elderly do need a Paleo (ie healthy) diet more than the young. Diabetes is much more dangerous than adipose tissue accumulation, so the elderly will suffer greater health impairment from an obesogenic (and diabetes-genic) diet than the young.

Is There Data Specifically Testing Rose’s Idea?

Rose’s idea that an evolved tolerance for toxin-rich diets will be specific to reproductively-aged persons with agriculturalist ancestors, is, so far as I know, not easily tested by available empirical evidence.

Studies in western populations alone will not be able to test Rose’s idea, because greater intolerance of toxic diets with higher age could simply be a result of an aging process that is universal in all populations. In order to find a process that recently evolved in agriculturalists, we would have to look at rates of aging or morbidity in different populations, both western and aboriginal, and see how aging rates or disease incidence depend on dietary toxicity:

  • Are Pacific Islanders more likely than westerners on similar diets to develop diabetes at reproductive ages, but equally likely at late ages? Are they more likely to become obese at younger ages than old?
  • Is aging more rapid in traditional peoples than in westerners during reproductive years, but similarly fast during elderly years, if they eat similar diets?

I am not aware of any such studies. Let me know if you are!

References

[1] Cassels S. Overweight in the Pacific: links between foreign dependence, global food trade, and obesity in the Federated States of Micronesia. Global Health. 2006 Jul 11;2:10. http://pmid.us/16834782.

[2] Unger RH, Scherer PE. Gluttony, sloth and the metabolic syndrome: a roadmap to lipotoxicity. Trends Endocrinol Metab. 2010 Jun;21(6):345-52. http://pmid.us/20223680. Sun K et al. Adipose tissue remodeling and obesity. J Clin Invest. 2011 Jun;121(6):2094-101. http://pmid.us/21633177.

[3] Health, United States, 2008: With Special Feature on the Health of Young Adults. National Center for Health Statistics (US). http://www.ncbi.nlm.nih.gov/books/NBK19623/.

[4] 2011 National Diabetes Fact Sheet, http://www.cdc.gov/diabetes/pubs/estimates11.htm.

Higher Carb Dieting: Pros and Cons

Posted by on February 2, 2012 160 comments

Last week’s post (Is It Good to Eat Sugar?, Jan 25, 2012) addressed what I see as the most problematic part of the thought of the health writer Ray Peat – his support for sugar consumption.

Apart from this difference, “an extreme amount of overlap is evident,” Danny Roddy notes, in our views and Peat’s. Both perspectives oppose omega-6 fats, support saturated fats, favor eating sufficient carbs to normalize metabolism, support eating nourishing foods like bone broth, and oppose eating toxic foods like wheat.

If there is another difference between our ideas and Peat’s, it’s that “Peat-atarians” often eat more carbs. Danny puts it:

Paul and Peat have similar recommendations for carbohydrate consumption. Paul’s recommendations hover around 150 grams while Peat usually recommends 180-250 grams, but he himself eats closer to ~400 grams.

So I thought it might be worth looking at the issue of overall carb consumption.

Carbs for Hypothyroidism

In Is There a Perfect Human Diet? (Jan 18, 2012) we noted that diseases can change the optimal diet. In some diseases it’s better to lower carb consumption, but in others it’s better to increase carb consumption. The example we gave is hepatitis; hepatitis B and C viruses can exploit the process of gluconeogenesis to promote their own replication, so high-carb diets which avoid gluconeogenesis tend to slow down disease progression.

Another disorder that might benefit from more carb consumption is hypothyroidism. A number of people with hypothyroidism have benefited from Peat-style carb consumption. Here is ET commenting on last week’s post:

As someone following the PHD with a good dash of Peat, I really enjoy this post and the comments. Thank you Paul….

Paul says that “I’m not persuaded that it’s a desirable thing to keep liver glycogen filled at all times, but for some health conditions it may be good to tend that way, like hypothyroidism.” Well, according to Chris Kresser, 13 of the top 50 selling US drugs are either directly or indirectly related to hypothyroidism. If going by either the low body temperature/low pulse diagnostic, and/or some kind of pattern on the serum tests (Anti-TG, TPO, TSH, free T-3, free T4, total T3, total T4), we are talking a significant proportion of the population, especially women, being hypothyroid in some form….

Many with low T3 have a conversion problem from T4 in the liver (80% of T3 is converted from T4 in the liver and kidneys – only a small portion is coming from the thyroid gland).

Is it a good idea to NOT try to fill the liver glycogen in such a pattern? For those who have lived with the consequences of low T3 (adrenaline rush, waking up in the middle of the night, fatigue, tendency to orange-yellowish color i the face etc.), and had improvements on a more Peat like diet, I do not think so.

The way to fill liver glycogen, of course, is by eating more carbs.

I’ve previously noted that increased carb consumption upregulates the levels of T3 thyroid hormone (Carbohydrates and the Thyroid, Aug 24, 2011):

T3, the most active thyroid hormone, has a strong effect on glucose utilization. T3 stimulates glucose transport into cells, and transport is the limiting factor in glucose utilization in many cell types. In hyperthyroidism, a condition of too much T3, there are very high levels of glucose utilization. Administration of T3 causes elevated rates of glycolysis regardless of insulin levels.

The body can reduce T3 levels by converting T4 into an inactive form called reverse T3 (rT3) rather than active T3. High rT3 levels with low T3 levels lead to reduced glucose transport into cells and reduced glucose utilization throughout the body.

This means that eating more carbs raises T3 levels, and eating fewer carbs lowers T3 levels.

For a hypothyroid person, then, eating more carbs is an alternative tactic for increasing thyroid hormone activity. It may provide symptomatic relief similar to that achieved by supplementing thyroid hormone directly.

Perhaps the two are complementary tactics that should be done together. Taking thyroid hormone pills will increase glucose utilization, creating a need to eat more carbs. A mix of the two tactics may be optimal.

UPDATE: Mario points out that most cases of hypothyroidism in advanced countries are due to Hashimoto’s, an autoimmune disease probably triggered by infections or gut dysbiosis, and eating more carbs will tend to flare any gut dysbiosis and thus aggravate the thyroiditis. Meanwhile, supplemental thyroid hormone tends to reduce antibody activity.

Carbs for Mood

Another interesting comment came from Jim Jozwiak:

Paul, this discussion gets to the crux of what I do not understand about the Perfect Health Diet. You are speaking as if refilling liver glycogen is a good thing, and it undoubtedly is, because mood is so much better when there is sufficient liver glycogen because then the brain is confident of its power supply. Also, you acknowledge that safe starch would eventually replenish liver glycogen after muscle glycogen is topped off. So why not eat enough starch to replenish liver glycogen? It is not so difficult to figure out how much that would be. Have some sugar, feel what replenished liver glycogen is like, then titrate safe starch gradually meal-by-meal to get the same effect. When I do it, and I am not an athlete, I get 260 grams of non-fiber carb per day, which is considerably more than you usually recommend. Have you tried this experiment and found the result unsatisfactory in some way?

Jim has experimented to find the amount of carbs that optimize his mood, and found it to be 260 g (1040 calories). On a 2400 calorie diet, typical for men, this would be 43% carbs.

If Peat typically recommends 180 to 250 g carbs, as Danny says, then on a 2000 calorie reference diet that would be 36% to 50% carbs.

Those numbers are strikingly similar to another statistic: The amount of carbs people actually eat in every country of the world.

Here is a scatter plot of carb consumption vs per capita income by country. Dietary data comes from the FAO, income is represented by GDP per capita from the IMF:

At low incomes people eat mainly carbs, because the agricultural staples like wheat, rice, corn, and sorghum provide the cheapest calories.

As incomes rise, carb consumption falls, but it seems to approach an asymptote slightly below 50% carbs. The lowest carb consumption was France at 45%, followed by Spain, Australia, Samoa, Switzerland, Iceland, Italy, Austria, Belgium, and Netherlands.

We can guess that if money were no object, and people could eat whatever they liked, most people would select a carb intake between 40% and 50%.

This is precisely the range which Jim found optimized his mood.

The Longevity vs Fertility and Athleticism Trade-off

I won’t enumerate studies here, but animal studies indicate that higher carb and protein intakes promote fertility and athleticism, while restriction of carbohydrate and protein promotes longevity.

In our book, we calculate the daily glucose requirements of the human body at around 600 to 800 calories, or 30% to 40% of energy on a 2000-calorie diet.

So a 30-40% carb diet is a neutral diet, which probably places minimal stress on the body.

A 40-50% diet is a carb-overfed diet, which probably promotes fertility and athleticism.

A 20-30% diet is a mildly carb-restricted diet, which probably promotes longevity.

Do we see diminished longevity with higher carb consumption in human epidemiological data? I think so.

It’s useful to compare European countries, since they are genetically and culturally similar. There is a correlation between carbohydrate intake and longevity. Here is a list of life expectancy among 46 European countries. Neglecting little countries like Monaco, San Marino, and Andorra, that are not in my carb database, the countries with the longest life expectancy are also the ones with the lowest carb consumption: Italy first, France second, Spain third, Switzerland fourth, and Iceland sixth are all countries with carb intake below 50%. Sweden, at 50.8% carbs, placed fifth in longevity.

Did Evolution Hardwire a Preference for Carbs?

We know that the brain has an innate food reward system which tries to get people to eat a certain diet. What carbohydrate intake is it likely to select for?

Experiments on the food preferences of insects and rodents give us clues. The paper “Macronutrient balance and lifespan,” by Simpson and Raubenheimer, cited some time ago by Dennis Mangan, summarizes evidence from animals for the influence of macronutrients on lifespan. A good example is the fruit fly; protein has the dominant effect on lifespan, with low protein favoring longevity and high protein favoring fertility. The flies eat so as to maximize fertility:

The response surface for lifetime egg production peaked at a higher protein content than supported maximal lifespan (1:4 P:C, Figure 1A). This demonstrates that the flies could not maximize both lifespan and egg production rate on a single diet, and raises the interesting question of what the flies themselves prioritized – extending lifespan or maximizing lifetime egg production. Lee et al. [3] answered this by offering one of 9 complementary food choices in the form of separate yeast and sugar solutions differing in concentration. The flies mixed a diet such that they converged upon a nutrient intake trajectory of 1:4 P:C, thereby maximizing lifetime egg production and paying the price of a diminished lifespan.

This seems to be the evolutionary preference in mammals as well as flies. When unlimited food is available, animals tend to overfeed slightly on carb and protein, sacrificing lifespan for increased fertility and athleticism.

Jim reported improved mood on a 43% carb diet. Is it due to the filling of liver glycogen raising metabolism? Due to a sensation of enhanced fertility, libido, and athleticism? Or simply due to greater satisfaction of the brain’s reward system?

Yet another factor may also be involved.

Might Stress Be Mistaken for Enhanced Energy?

Peat favors sucrose as a carb source, which is why Danny Roddy recommended orange juice and Travis Culp soda. I argued in last week’s post that it would be better to eat a starchier diet so that the carb breakdown would be at least 70% glucose, less than 30% fructose and galactose.

Eating a higher-carb diet fills up liver glycogen, removing the most rapid fructose disposal pathway. This makes a high-carb sucrose-based diet rather stressful for the body; it has to dispose of fructose rapidly to avoid toxicity, but has limited ability to do so.

We can see the stressfulness of sucrose by its effects on the “fight-or-flight” stress hormones adrenaline (epinephrine) and noradrenaline (norepinephrine). Here is a study that fed high-fat, high-starch, and high-sucrose diets for 14 days to healthy non-obese subjects, and measured the hormonal response [1; full text]. This paper was discussed by the blog Proline (hat tip: Vladimir Heiskanen). The results:


On high-fat and high-starch diets, adrenaline and noradrenaline levels are low; they are consistently elevated — almost doubled — on the high-sucrose diet.

This makes sense; as Wikipedia notes,

epinephrine and norepinephrine are stress hormones that underly the fight-or-flight response; they increase heart rate, trigger the release of glucose from energy stores, and increase blood flow to skeletal muscle.

These hormones trigger the release of glucose from liver glycogen, thus freeing up room for fructose disposal.

Note that this result contradicts an assertion by Danny Roddy:

I consider the ability to refill glycogen (minimizing adrenaline & cortisol release) to be an important factor in health.

Refilling glycogen is not the same thing as minimizing adrenaline release. The requirement to dispose of fructose may trigger adrenaline release.

The reason I bring this up is not to renew the starch vs sugar discussion; but rather to ask if this “fight-or-flight” response to sugar consumption may not be partially responsible for the perceived mood and energy improvements on a Peat-style diet.

Indeed, one of the peculiar aspects of Ray Peat’s health advice is his recommendation to increase pulse rates well above normal levels. In his article on hypothyroidism, Peat states:

Healthy and intelligent groups of people have been found to have an average resting pulse rate of 85/minute, while less healthy groups average close to 70/minute.

I would have thought 60 beats per minute was normal, and when I was more athletic my pulse was typically 48 beats per minute.

One of the effects of adrenaline and noradrenaline is to speed up the pulse rate. If Peat really does eat 400 g of carbs per day, predominantly from sucrose, then he may be achieving his high pulse rate from an “adrenaline rush” that helps dispose of an excess of fructose.

If, indeed, this is a source of improved sense of well-being on Peat-style diets, it may be a double-edged sword. Chronic stimulation of the “fight-or-flight” hormones to aid in fructose disposal may have long-run negative consequences.

UPDATE: I’m reminded of this video, showing the adrenaline-promoting effects of sucrose consumption:


Starch would not have had the same effect, and would surely be healthier in the long run.

Summary

It is possible that higher carb intake may increase thyroid hormone levels, fertility, and athleticism, and enhance mood in some people. These gains do not come without cost. Notably, they probably involve a sacrifice of longevity.

If the benefits of higher carb intake are sought, it is best to achieve them by eating starches primarily, not sugar.

Conclusion

In our book, we recommend a slightly low-carb diet of 20-30% of calories. If we were re-writing the book now, we would probably be a bit less specific about what carb intake is best. Rather, we would say that a carb intake around 30-40% is neutral and fully meets the body’s actual glucose needs; and discuss the pros and cons of deviating from this neutral carb intake in either direction.

For most people, I believe a slightly carb-restricted intake of 20-30% of calories is optimal. Most people are not currently seeking to have children or engaging in athletic competition. There is good reason to believe that mild carb restriction maximizes lifespan, and most people desire long life. As we’ve noted, supercentenarians generally eat low-carb, high-fat diets.

But the spirit of our book is to educate, and let everyone design the diet that is best for them. And there is room for difference of opinion about the optimal carb intake.

References

[1] Raben A et al. Replacement of dietary fat by sucrose or starch: effects on 14 d ad libitum energy intake, energy expenditure and body weight in formerly obese and never-obese subjects. Int J Obes Relat Metab Disord. 1997 Oct;21(10):846-59. http://pmid.us/9347402. Full text: http://www.nature.com/ijo/journal/v21/n10/pdf/0800494a.pdf.