Monday, July 2, 2012

The lowest-mortality BMI: What is the role of nutrient intake from food?

In a previous post (), I discussed the frequently reported lowest-mortality body mass index (BMI), which is about 26. The empirical results reviewed in that post suggest that fat-free mass plays an important role in that context. Keep in mind that this "BMI=26 phenomenon" is often reported in studies of populations from developed countries, which are likely to be relatively sedentary. This is important for the point made in this post.

A lowest-mortality BMI of 26 is somehow at odds with the fact that many healthy and/or long-living populations have much lower BMIs. You can clearly see this in the distribution of BMIs among males in Kitava and Sweden shown in the graph below, from a study by Lindeberg and colleagues (). This distribution is shifted in such a way that would suggest a much lower BMI of lowest-mortality among the Kitavans, assuming a U-curve shape similar to that observed in studies of populations from developed countries ().

Another relevant example comes from the China Study II (see, e.g., ), which is based on data from 8000 adults. The average BMI in the China Study II dataset, with data from the 1980s, is approximately 21; for an average weight that is about 116 lbs. That BMI is relatively uniform across Chinese counties, including those with the lowest mortality rates. No county has an average BMI that is 26; not even close. This also supports the idea that Chinese people were, at least during that period, relatively thin.

Now take a look at the graph below, also based on the China Study II dataset, from a previous post (), relating total daily calorie intake with longevity. I should note that the relationship between total daily calorie intake and longevity depicted in this graph is not really statistically significant. Still, the highest longevity seems to be in the second tercile of total daily calorie intake.

Again, the average weight in the dataset is about 116 lbs. A conservative estimate of the number of calories needed to maintain this weight without any physical activity would be about 1740. Add about 700 calories to that, for a reasonable and healthy level of physical activity, and you get 2440 calories needed daily for weight maintenance. That is right in the middle of the second tercile, the one with the highest longevity.

What does this have to do with the lowest-mortality BMI of 26 from studies of samples from developed countries? Populations in these countries are likely to be relatively sedentary, at least on average, in which case a low BMI will be associated with a low total calorie intake. And a low total calorie intake will lead to a low intake of nutrients needed by the body to fight disease.

And don’t think you can fix this problem by consuming lots of vitamin and mineral pills. When I refer here to a higher or lower nutrient intake, I am not talking only about micronutrients, but also about macronutrients (fatty and amino acids) in amounts that are needed by your body. Moreover, important micronutrients, such as fat-soluble vitamins, cannot be properly absorbed without certain macronutrients, such as fat.

Industrial nutrient isolation for supplementation use has not been a very successful long-term strategy for health optimization (). On the other hand, this type of supplementation has indeed been found to have had modest-to-significant success in short-term interventions aimed at correcting acute health problems caused by severe nutritional deficiencies ().

So the "BMI=26 phenomenon" may be a reflection not of a direct effect of high muscularity on health, but of an indirect effect mediated by a high intake of needed nutrients among sedentary folks. This may be so even though the lowest mortality is for the combination of that BMI with a relatively small waist (), which suggests some level of muscularity, but not necessarily serious bodybuilder-level muscularity. High muscularity, of the serious bodybuilder type, is not very common; at least not enough to significantly sway results based on the analysis of large samples.

The combination of a BMI=26 with a relatively small waist is indicative of more muscle and less body fat. Having more muscle and less body fat has an advantage that is rarely discussed. It allows for a higher total calorie intake, and thus a higher nutrient intake, without an unhealthy increase in body fat. Muscle mass increases one's caloric requirement for weight maintenance, more so than body fat. Body fat also increases that caloric requirement, but it also acts like an organ, secreting a number of hormones into the bloodstream, and becoming pro-inflammatory in an unhealthy way above a certain level.

Clearly having a low body fat percentage is associated with lower incidence of degenerative diseases, but it will likely lead to a lower intake of nutrients relative to one’s needs unless other factors are present, e.g., being fairly muscular or physically active. Chronic low nutrient intake tends to get people closer to the afterlife like nothing else ().

In this sense, having a BMI=26 and being relatively sedentary (without being skinny-fat) has an effect that is similar to that of having a BMI=21 and being fairly physically active. Both would lead to consumption of more calories for weight maintenance, and thus more nutrients, as long as nutritious foods are eaten.


dearieme said...

Can you explain, please, how age is allowed for in these data?

I mean, people tend to become fatter as they age, and their remaining lifespan shortens. Clearly this effect must somehow be subtracted out or it will confound the effect you want to study.

Ned Kock said...

Usually in BMI studies the baseline measures are collected many years before death, and then the participants are followed for a period of time (e.g., 20 years) or until death – what is called a “prospective cohort study”.

dearieme said...

Thanks. But if you start following someone's weight from, say, age 20, you'll get very different results from starting at age 40. Won't you?

Unknown said...

Thanks Ned, I greatly value your approach and all your articles. I've linked permanently to this one from my site as a neat explanation of how bodybuilding may help contribute to lower mortality/higher health expectancy/longevity, though as you point out it may not be necessary to reach b/b levels of muscularity in order to benefit. Much other evidence also confirms that supplements are no substitute for food: see notes 26-37 in this link for references

Wishing you lifelong health, naturally, Ivor

Ned Kock said...

Hi dearieme. Yes, I think so, but if you start a study a an early age you’ll have to wait a long time to have enough deaths for meaningful categorization.

Sometimes data collection decisions are driven by convenience of analysis.

In the previous post we’ve seen that even following from 50 years of age leads to some difficulties in that respect – you have to study thousands of people.

Ned Kock said...

Thanks Ivor.

Puddleg said...

This is a good explanation for this effect.
The water-soluble vitamins are mainly used to metabolise the macronutrients, so needs are relative; the fat-soluble vitamins and EFAs function more like regulatory factors; and electrolytes would also be optimised at muscle BMI intakes.
I think Bruce Ames would appreciate your hypothesis.

Ned Kock said...

Thanks for commenting and for the tip George. There is an interesting article by Bruce Ames here:

dearieme said...

That Ames article is fascinating: thank you for the tip.

Anonymous said...

How would the results look like if ^3 was used for BMI instead of ^2? I'm not a two dimensional construct.

Blue Cross of California said...

Thanks for that additional info, it adds a lot. Obesity has been shown to be heritable, but most studies predate the onset of the "obesity epidemic" that has been rampant over the last twenty years.

Jillian said...


I have a quick question about your blog, do you think you could email me?


Ned Kock said...

Hi Anon, using height^3 would make the measure something other than what is known as the BMI.

Also, since humans are not square-shaped, using height^3 would grossly overestimate volume, don’t you think?

dearieme said...

Weight divided by height^3 would yield a measure of density. Which might, I suppose be relevant - but still suppresses all questions involved in comparing, say, the person built like a pipe cleaner and the person with broad shoulders, bull chest, wide hips, or whatever.

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