Monday, July 15, 2013

How can carrying some extra body fat be healthy?

Most of the empirical investigations into the association between body mass index (BMI) and mortality suggest that the lowest-mortality BMI is approximately on the border between the normal and overweight ranges. Or, as Peter put it (): "Getting fat is good."

As much as one may be tempted to explain this based only on the relative contribution of lean body mass to total weight, the evidence suggests that both body fat and lean body mass contribute to this phenomenon. In fact, the evidence suggests that carrying some extra body fat may be healthy for many.

Yet, the scientific evidence strongly suggests that body fat accumulation beyond a certain point is unhealthy. There seems to be a sweet spot of body fat percentage, and that sweet spot may vary a lot across different individuals.

One interesting aspect of most empirical investigations of the association between BMI and mortality is that the participants live in urban or semi-urban societies. When you look at hunter-gatherer societies, the picture seems to be a bit different. The graph below shows the distribution of BMIs among males in Kitava and Sweden, from a study by Lindeberg and colleagues ().

In Sweden, a lowest mortality BMI of 26 would correspond to a point on the x axis that would rise up approximately to the middle of the distribution of data points from Sweden in the graph. It is reasonable to assume that this would also happen in Kitava, in which case the lowest mortality BMI would be around 20.

One of the key differences between urbanites and hunter-gatherers is the greater energy expenditure among the latter; hunter-gatherers generally move more. This provides a clue as to why some extra body fat may be healthy among urbanites. Hunter-gatherers spend more energy, so they have to consume more “natural” food, and thus more nutrients, to maintain their lean body mass.

A person’s energy expenditure is strongly dependent on a few variables, including body weight and physical activity. Let us assume that a hunter-gatherer, due to a reasonably high level of physical activity, maintains a BMI of 20 while consuming 3,000 kilocalories (a.k.a. calories) per day. An urbanite with the same height, but a lower level of physical activity, may need a higher body weight, and thus a higher BMI, to consume 3,000 calories per day at maintenance.

And why would someone want to consume 3,000 calories per day? Why not 1,500? The reason is nutrient intake, particularly micronutrient intake – intake of vitamins and minerals that are used by the body in various processes. Unfortunately it seems that micronutrient supplementation (e.g., a multivitamin pill) is largely ineffective except in cases of pathological deficiency.

Urbanites may need to carry a bit of extra body fat to be able to have an appropriate intake of micronutrients to maintain their lean body structures in a healthy state. Obviously the type of food eaten matters a lot. A high nutrient-to-calorie ratio is generally desirable. However, we cannot forget that we also need to eat fat, in part because without it we cannot properly absorb the all-important fat-soluble vitamins. And dietary fat is the most calorie-dense nutrient of all.

Why not putting on extra muscle instead of carrying the extra fat? For one, that is not easy when you are a sedentary urbanite. Particularly after a certain age, if you try too hard you end up getting injured. But there is another interesting angle to consider. Humans, like many other animals, have genetic “protections” against high muscularity, such as the protein myostatin. Myostatin is produced mostly in muscle cells; it acts on muscle, by inhibiting its growth.

Say what? Why would evolution favor something like myostatin? Big, muscular humans could be at the top of the food chain by physical strength alone; they could kill a lion with their bare hands. Well, it is possible. (Many men like to think of themselves as warriors, probably because most of them are not.) But evolution favors what works best given the ecological niches available. In our case, it favored bigger and more plastic brains to occupy what Steve Pinker called a “cognitive niche”.

Even though fat mass is not inert, secreting a number of hormones into the bloodstream, the micronutrient “need” of fat mass is likely much lower than the micronutrient need of non-fat mass. That is, a kilogram of lean mass likely puts a higher demand on micronutrients than a kilogram of fat mass. This should be particularly the case for organs, such as the liver, but also applies to muscle tissue.

While gaining muscle mass through moderate exercise is extremely healthy, bulking up beyond one’s natural limitations may actually backfire. It could increase the demand for micronutrients above what a person can actually consume and absorb through a healthy nutritious diet. Some extra fat mass allows for a higher level of micronutrient intake at weight maintenance, with a lower demand for micronutrients than the same amount of extra lean mass.

Some people are naturally more muscular. Their frame and underlying organ-based capabilities probably support that. It is often visibly noticeable when they go beyond their organ-based capabilities. A common trait among many professional bodybuilders, who usually go beyond the genetic gifts that they naturally have, is an abnormal swelling of internal organs.

What complicates this discussion is that all of this seems to vary from individual to individual. People have to find their sweet spots, and doing that may not be the simplest of tasks. For example, even measuring body fat percentage with some precision is difficult and costly. Also, certain types of fat are less desirable than others – visceral versus subcutaneous body fat. It is not easy differentiating one from the other ().

How do you find your sweet spot in terms of body fat percentage? One of the most promising approaches is to find the point at which your waist-to-weight ratio is minimized ().


ProudDaddy said...

You might be interested in a July 2013 PLOS ONE article by Wilson et al. regarding "Ratio of Trunk to Leg Volume...". It's based on NHANES data. I found the data for NORMAL BMI subjects particularly interesting!

Bill said...

Interesting post, Ned.
I like this view of the trade-off: either high physical activity or excess fat mass is required to buffer nutrient-poor calories.

dearieme said...

Age? Sex? Race? Do none of them matter?

Second point: mostly in optimisation problems the question isn't really which parameter values optimise the objective function: it's how far you can stray from those values without substantially impairing the objective function. In other words, do you face a "flat" optimum?

Jack C said...

Excessive consumption of polyunsaturated fats (PUFA), particularly n-6 linoleic acid(LA), leads to impairment of thyroid function (hypothyroidism) which results in reduced energy expenditure and increased weight gain per calorie of food intake.

PUFA intake has increased threefold in the the last century. The percentage of n-6 HUFA (arachidonic acid, AA)in red blood cells has increased to 77% in the U.S. compared to 51% in Japan. The obesity rate in the U.S. is now 37% compared to 3% in Japan.

The difference in red blood cell AA between the U.S. and Japan of 26% (77% - 51%) approximates the increase in a study where mice where fed diets with either 1% or 8% LA as % of calories. On the high LA diet, energy expenditure decreased by 14%, food intake decreased by 2%, weight increased by 12% and the adiposity index increased by 25% due to the fact that the increased weight went to adipose tissue.

Obviously the important weight to height ratio can be minimized by reducing intake of LA and aiming for a goal of 50% n-6 as % of HUFA.

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Jack C said...

To clarify the foregoing regarding the effect of increased n-6 LA on obesity, the high LA rodent diet of 35% of calories as fat, 1% as n-3 ALA and 8% as n-6 LA approximates the average diet in the U.S. today. The low LA rodent diet of 1% ALA and 1% results in the same percentage of n-6 AA in HUFA as the Japanese diet today. The higher rate of obesity in the U.S. compared to Japan is attributable mainly to increased weight gain per calorie of food intake due to impaired thyroid function caused by high LA.

The imbalance of intake of PUFA results in adverse health consequences because animals can not synthesize PUFA as they due other fats. LA is the precursor to ALA which is the precursor to n-6 eicosenoids, signalling molecules that control many complex bodily systems. Imbalanced PUFA intake causes dysregulation of eicosenoid controlled metabolism.

The particular eicosenoids that apparently impair thyroid function are endocannabinoids, anandamide and 3-AG which are derived from arachidonic acid, n-6 AA. Elevation of AA due to increased LA intake results in increased endocannabinoids and causes the impairment of thyroid function.

Nils said...

Hi Ned, solid post as usual, though you have posited this theory before.

What is your take on the discrepancy betweenthe optimum micronutrient intake with the promising results of caloric restriction on lifespan though?

Greetings, Nils

Ned Kock said...

Hi dearieme. I am not sure I understand the question.

Ned Kock said...

Hi Jack. Did you mean to say “weight to height ratio”? This would be essentially a measure of waist size in adults.

Ned Kock said...

Hi Nils. I have a post on this here:

Anonymous said...

Great post Ned.

Question: Why would those who went beyond their genetic capacity in gaining muscle mass have swelling of the organs, if you also say it may not be possile for these people to get sufficient micronutrient intake due to their excess of muscle tissue?

Put differntly, is swelling of the organs consistent w/ insuffcient micronutirent intake? Or am I connecting things that are totally unrelated? Or does the causation run the other way: swelling indicates insufficeint nutrient intake.

Really enjoying this series, Ned, and it's nice to see you blogging more frequently.

Jack C said...

Ned, I erred. I meant to say waist to weight ratio which of course is what you suggest is a good measure of optimal weight. I agree with your take on the matter.

The hypothyroidism induced by excessive intake of LA from vegetable oils results in increased weight gain per calorie of food intake and that weight gain is preferentially directed to belly fat which increases waist to weight ratio.

Hypothyroidism is also associated with increased risk of non-alcoholic fatty liver disease NAFLD) and insulin resistance

Regarding intake of fat soluble vitamins, it is noted that during the last century intake of animal fats has decreased from 80% to 40% of fat calories resulting in about a 50% decrease in intake of fat soluble vitamins. Decreased vitamin K2 intake alone results in significantly increased mortality from CHD and certain cancers (lung cancer and prostate cancer).

Unknown said...

what about which refutes the cornerstone of the blog post which, i.e the assumption that hunter gatherers expend more and this is why their high caloric/nutrient intake leads to a leaner body profile than a more sedentary urbanite culture. Seems like it's something else, although I also tend to feel that it's better to keep yourself in a mode of being able to consume a lot to ensure nutrient sufficiency from real foods.

dearieme said...

"How can carrying some extra body fat be healthy?"

How do we know what's "extra"?

Jack C said...

Your website seems to have some kind of virus for when I log on to the site I am usually redirected to some other site. A few minutes ago I was redirected to something like "fungames". If I immediately click off and then go back to the site I usually can log on with no further redirection. This happens with both my computers which have different e-mail addresses.

Ned Kock said...

Hi Anon. Benign organ enlargement is commonly associated with weight gain, particularly when weight gain is due primarily to muscle gain, and other factors – e.g., increased physical activity. It seems to be associated with organ load.

Ned Kock said...

Hi Unknown. From the paper you referenced:

“… physical activity level, PAL, was greater among Hadza foragers than among Westerners. Nonetheless, average daily energy expenditure of traditional Hadza foragers was no different than that of Westerners after controlling for body size.”

In other words, the Hadza were lean and physically active. The energy expenditure in Westerners was primarily due to their greater body size. Exactly the point made here.

Ned Kock said...

Hi dearieme. Since I am writing in English, some level of imprecision is unavoidable. If I use too many math equations this blog will be useless to most.

Ned Kock said...

Actually, this blog already has a reputation of being a “mental workout” as it is, even as I try to avoid too much technical jargon.

Ned Kock said...

Hi Jack. I thought that had been addressed. The Google folks told me that the problem was solved. I’ll check again.

hellojtm said...

"“… physical activity level, PAL, was greater among Hadza foragers than among Westerners. Nonetheless, average daily energy expenditure of traditional Hadza foragers was no different than that of Westerners after controlling for body size.”

In other words, the Hadza were lean and physically active. The energy expenditure in Westerners was primarily due to their greater body size. Exactly the point made here."

whoops. i think you're right. Sorry that my posts come in as Anon, i'm logging in via google so I have updated my username to make responses more meaningful.

It seems that the folks that previously sent me that study, and summarized it, missed the basic point that the expenditure is the same but not for the same reason. Thanks for not slamming me for that oversight. ;)


WilliamS said...

"Benign organ enlargement is commonly associated with weight gain, particularly when weight gain is due primarily to muscle gain, and other factors – e.g., increased physical activity. It seems to be associated with organ load."

It may more more than just "benign." As you may know, Ned, Dr. Doug McGuff (Body By Science) is in the unique position of both owning a strength training studio (HIT) and working as an emergency physician.

He sees a lot of CAT (and other) scans. He has reported (based at least in part on his own wife's case I believe), that longtime HIT strength training practitioners have significantly larger internal organs.

He believes this is a very positive global adaptation to properly exercising skeletal muscles, and that should one find oneself fighting for life in an ICU with a critical illness or injury all that extra physiological "headroom" could make the difference.

Ned Kock said...

Hi WilliamS. Another factoid in support of Doug’s position is this: people under prolonged fasting (e.g., 30 days) tend to die from organ failure, not from lack of fat as a source of energy. This is in part due to amino acid depletion in the organs, including the heart.

The body always consumes some glucose during prolonged fasting, even though that tends to go down over time, as ketosis ramps up. After liver glycogen is depleted, glucose production relies heavily on amino acids. This includes amino acids stored in organs.

Even a lean 150-lb person, at 10 percent body fat, will have enough stored fat to survive for more than 30 days and still have plenty left. The problem is that this person may not be able to retain enough lean body mass, part of which will be used for glucose production, at that body fat percentage.

In other words, considered in isolation, lean body mass is more important for survival than body fat. But some level of body fat is needed to retain enough lean body mass; with variations across individuals. Here we go again, the waist-to-weight ratio theory.

Anonymous said...

Still waiting on your denunciation of Nikoley. Then - and maybe then - we can engage in a productive discussion.

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Ned Kock said...

Hi Anon. I am not sure I understand - “Still waiting on your denunciation of Nikoley”???

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Sophia John said...

I like this view of the trade-off: either high physical activity or excess fat mass is required to buffer nutrient-poor calories.
.Thank You.

Zorica Vuletic said...


I do notice out of the category of 'way too thin/anorexic' women (sorry I am focusing on women for this example and I know males can be the same) that the ones who are 'chronic exercisers' do tend to be better off health-wise. They tend to look 'less' ill, 'less' bad skin etc. I in fact saw two way too skinny women walking side by side and I could definitely tell the one who was chronic exerciser vs. just plain starving themselves. lol Kind of interesting to see the two side by side.

I do believe that for men if they are way too thin and don't eat it really is regarded differently and/or discarded. Either one assumes they have a 'fast metabolism' or they are viewed as alcoholics/drug users. There doesn't seem to be the 'anorexic' label attached to them, even though they are in fact, anorexic. lol

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Anonymous said...

Having some body fat actually increases your leg muscules (as compared to being thing) assuming the moving habits don't change.

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