Friday, April 11, 2014

More Graphs of Calorie Intake vs. BMI

In the last post, a reader commented that the correlation would be more convincing if I graphed calories vs. average BMI rather than the prevalence of obesity.  It was a valid point, so I went searching for average BMI values from NHANES surveys.  I dug up a CDC document that contains data from surveys between 1960 and 2002 (1).  Because these data only cover five survey periods, we only get five data points to analyze, as opposed to the eight used in the last post.  The document contains BMI values for men and women separately, so I averaged the two to approximate average BMI in the general adult population.  It's also worth noting that I use the approximate midpoint of the survey period as the year.

First, a graph of average BMI over time.  It went up:

Now, let's see how well average BMI correlates with calorie intake:

The correlation between calorie intake and obesity prevalence was remarkable, but this correlation is simply incredible.  An R-squared value of 0.98 indicates that daily calorie intake and average BMI are almost perfectly correlated.

We can further deduce that each 100-calorie increase in daily food intake is associated with an 0.62-point increase in average BMI among US adults.  


Kindke said...

I was just wondering, total energy expenditure also increases with BMI (for ex as in the below study _) and body mass, so maybe it could be inferred that the increased caloric intake of higher BMI individuals is a consequence of their higher energy expenditure requirements?

I.E. they are eating enough food to satisfy their energy needs to keep them weight stable.

Twenty-Four Hour Total and Dietary Fat Oxidation in Lean, Obese and Reduced-Obese Adults with and without a Bout of Exercise

g-mo said...

Fascinating. I would love to see a scatter plot with more points. Perhaps with some data from other countries?

I think it's worth comparing your regression equation to the Mifflin St Jeor equation. That formula is:

BMR kcal/day = 10.0m + 6.25h - 5.0a + s

where m is weight in kg, h is height in cm, a is age, and s is an adjustment factor for sex (+5 for men, -161 for women).

If you plug in the average weight, height, and age of Americans (82 kg, 169 cm, and 38 years), and use an average s of -78, you get a BMR of around 1600. According to the Wikipedia page on BMR, you can roughly adjust BMR to maintenance intake by dividing by 0.7, which gets you around 2300.

Using your equation, 2300 calories is associated with a BMI of around 25, versus the observed average BMI of Americans of 28.

valerie said...

Thank you!

Now, can someone explain how 100 more calories can lead to only 0.62 more points of BMI? Roughly, that would mean about 4 pounds gained for a daily increase of 100 calories. I would have expected something closer to 10 pounds. Unless average height increased (a lot)? Or a large chunk of the population can eat more without gaining weight?

Mmmm said...

The problem is still, what those calories are comprised of. Calories did increase, but it wasn't calories from butternut squash or wild caught salmon that increased.

If people added 500 calories to their diet from wild caught fish, and vegetables, then it could have a very different result from those getting an extra 500 calories from donuts, and pepsi.

Stephan Guyenet said...

Hi Kindke,

Very good thought. I think you're right. Energy requirements do increase with BMI, and so does appetite (although the evidence here is not that clear-- what is clear is that they eat more, whether or not due to higher appetite). I think there are elements of both forward and reverse causation in the data. Still, the elevated calories are a requirement for the elevated BMI.

Hi Valerie,

I'd have to plug the numbers into the NIH body weight simulator to give you a good answer. However, these data are not as clean as I'd like them to be because there are other changes (e.g. physical activity) that are co-occurring but not controlled for. That could mean the numbers don't line up perfectly with expectations.

Hi Garrett,

Thanks. The kcal intake data could be systematically a bit elevated, it depends on the accuracy of the value that I used to adjust gross sales for loss between sale and consumption. The ERS estimates 28.8% loss, but if waste is greater then actual kcal intake would be systematically lower throughout the data set.

Anonymous said...

If correct, this study is perplexing:
It claims that as teenagers ate more junk over the period 1965-1996, their energy intake decreased.

Anonymous said...

Hi Stephan ,

Good article, as usual. :)

I just wish doctors would measure body fat specifically in patients , instead of use the BMI. Perhaps a DEXA scan would reveal the true level of adiposity? There may be better options. I am fairly sure all would be expensive and not practical at the moment. I am not real familiar with the most accurate measures of human body fat levels. Nonetheless, it would be a far better true measure of how fat somebody actually is.

Back in his prime Bo Jackson would be classified as obese when he was anything but.he had perhaps one of the greatest physiques in history,. Conversely, I am sure a seemingly thin to normal weight person , who actually has a substantial mount of body fat ( called normal weight obesity) would be classified as normal and healthy.

In my honest opinion the BMI must go. Sooner the better.

I recently came up with something that I feel is useful ( but somewhat silly and funny) to understand things better.

I think of it in "human meat" terms. Some people are sirloin ( think prime Bo Jackson, Deion Sanders, Evander Holyfield etc.) Others are more like rib eye. And even more are like baloney and salami. What makes this so? What explains all of this fat tissue that remains - even intramuscular fat that remains -when obese people "lose weight" ? Why do they so often still have tremendously fatty legs etc. even though they are smaller in overall size. A naturally lean person's thigh will look totally different- hard and defined - even if the reduced weight obese person has a similar body size in their leg?.

I know this is funny, but it is useful: If there were aliens who came to Earth, and loved to eat fatty human meat , and had advanced systems for accurately measuring true adiposity levels- then guys like prime Deion Sanders would be completely avoided , while "successful" gastric bypass patients ( who are really full of fat despite looking smaller in size) would be targeted immediately and eaten. Even if these people were similar in size to Deion, they are nowhere remotely as lean. Not even close.

Bo Jackson was bigger than Deion but almost as lean. Compared to trumpeted "successful" gastric bypass surgery patients , Bo Jackson was a very lean and BIG piece of sirloin while they are a much smaller piece of salami or baloney etc. Deison was a smaller piece of sirloin. At best, these people might get to a fatty cut of rib eye, but it is rare. The result is usually a big piece of salami to a tinier piece of salami- losing some , bone mass, organ mass, muscle mass and fat mass too etc. but they are still significantly fat. it is the best we have, but it is not effective enough. I sympathize with them.

Bo Jackson did not even lift weight at all. LOL ! Arnold did though.

Genes have much to say, and various complex biochemical/physiological factors, too. Obviously, anabolic steroid drugs which most pro bodybuilder use etc. also went into it as well. ;) :) LOL !

As we know, and as Dr. Jeffrey Friedman points out, energy is necessary requirement to induce obesity ( but not sufficient). Nobody is going to become tremendously obese on a desert island with almost no chemical energy from food available.

But, how this chemical energy is handled, the pathways it is led to etc. matter a lot.

The caloric hypothesis, by itself, cannot account for this and sufficiently explain body fat mass regulation because it is highly complex.

All interesting stuff. I hope scientists get a much deeper understanding of obesity and fat cell regulation at the molecular level in the future.

I am just putting thoughts out there. It's not for answers necessarily :)

Keep up the great work, Stephan. Your recent articles are great. I just thought I'd share for the masses one last time until I go back into my retirement ( laughs).

Wishing you the best,buddy.

Mirrorball said...

Bear in mind that with fewer points it's easier to fit them in a line so you will get a higher R^2.

Unknown said...

Did the constitution of the calories change during that period? Were the rising calorie counts from processed foods? We need to be careful because as we know, correlation does not imply causation.

glib said...

Hence the value of a fat centered diet, with supplementation of fermentable fiber (resistant starch). Both give a sense of satiety, RS particularly so.

Anonymous said...

I have a set of dinnerware from the 1950s and one recently purchased. The dinner plate from the new set is 1.75in larger than the old plate. In the 1960s a McD hamburger was made from 1.6oz of beef. Two liter soda bottles were introduced in the early 70s to augment the 6-8oz bottles then available. In the 60s and 70s people moved from the city to the suburbs in droves and car commuting became the norm. In the 70s more mothers began going to work and three sit down meals daily became far less common. Calorie intake has gone up, calorie expenditure has gone down, so the cause of increasing obesity since we began seeing these cultural changes must be ... wheat.

Sara said...

Stellar, I've noticed the same thing. I have my great-grandmother's crockery and everything is tiny, including the teacups, compared to today. It's also very pretty. Mealtimes (and 'tea-times') were always so ceremonial at her place.

Modern crockery is huge, and industrial looking. Let's fight for a return of small and pretty plates!

Unknown said...

Maybe calorie intake is only relevant in the context of a compromised gut biome -

Gorillas living at the zoo doubled their calorie intake but lost an average of 65 pounds after adopting an evolutionarily compatible diet.
In doing so that presumably changed their gut biome as well.

exchanging the gut biome of skinny and obese mice turns the skinny mice obese and the obese mice skinny without modulating calorie intake -

It's possible that calories are closely associated with BMI in modern humans because a disregulated gut biome is ubiquitous among us.
It's probable that restoring a healthy gut biome and adopting a paleo friendly diet would foster a healthy BMI irrespective of calorie intake, which would explain why some primitive tribes remain lean despite eating a high calorie diet.

Robert said...

Hi Dr. G,

Regarding altitude and obesity, there's a new study in PLOS ONE from the Air Force (where I'm headed) that found that high altitude living reduced odds that overweight servicemen and women became obese by ~40%.

Unknown said...

Seeing as we are not a fire or an internal combustion engine, and we do not incinerate what we consume, let's discard the notion of "burning calories" and calories in general.

MACRONUTRIENTS, not calories, are what we are talking about, here.

Now that we are focused on the constituents themselves, rather than the measure of their thermal release upon incineration, we have a clearer understanding of the quality perspective.

Also, these macronutrients (and micronutrients, phytonutrients, etc) are what our body uses to build and repair all of our cells. These chemical processes can not be equated with burning these nutrient compounds in a fire and none of our bodily processes are powered by thermal energy anyway so the use of Caloric measurement of food is irrelevant, archaic science and is really quite silly at this point.

So, to be clear, what we're talking about here is the correlation between macronutrient intake and BMI.

The commenter "Mmmm" made the most relevant point in this entire discussion.

It isn't about quantity, it's about quality.

As a scientist, you understand the scientific process and the necessity of reducing the range of study to one variable.

The problem is, you have two variables here: Macronutrients and toxins (a whole host of compounds that cause irritation, inflammation, hormone deregulation, and damage in your body)

As you increase your macronutrient intake, your body increases the performance of many bodily processes to accommodate and utilize the extra nutrients. This will have an impact on BMI as you'll gain lean muscle. (In highschool they said I was overweight...I had a sixpack and was a star athlete..just goes to show how flawed the establishment line on health is)

As you increase your toxin intake, on the other hand, your body will, naturally, store more toxins in a certain type of fat cells whose purpose is to trap these compounds that your body doesn't recognize and/or recognizes as being harmful to your other tissues.

So, this is the dilemma. You have an increase/decrease of good macronutrients and an increase/decrease of accompanying toxins. Two variables do not produce accurate scientific observations.

If you increase macronutrients and toxins, together, from low quality food (as in your study) you will, certainly, see an increase in BMI, and as long as this type of low quality, high toxin diet is maintained, their BMI will continue to rise, as their bodies protective systems continue to store these toxins, though the macronutrient ratios and types of toxins will determine body composition, which is actually a marginally useful measure, if only for entertainment purposes, whereas BMI is not really useful for anything.

I digress.

To the point: if you increase your macronutrient intake from high quality (high macronutrient, low toxin) food, you will detox those cells as well as decrease inflammation. You will lose the "fat" weight, but gain lean muscle weight, improving your body composition and, irrelevantly, also affecting your BMI. Depending on your body composition before and after your transformation, your BMI might go up if you gained more pounds of lean muscle than you removed in pounds of "fat", or, conversely, your BMI would, expectedly, decrease, if you removed more pounds of "fat" than you gained in pounds of lean mass.

The moral of the story is that it is imperative that we stop focusing on HOW MUCH we eat, and focus on what really matters, WHAT we eat.

Eat high quality, low toxin foods. Eat until you are satisfied. Life doesn't have to be so damn complicated.


Stephan Guyenet said...

Hi Reece,

Nonsense. The only attribute of food that has been convincingly shown to influence body fatness in humans is the number of calories that can be absorbed from it. Studies to date suggest that calories from carb, fat, and even protein are approximately interchangeable when it comes to body fatness. There is no evidence that our current diet contains "toxins" that prevent us from burning off extra energy.

It's possible, even likely, that we'll eventually show that food properties besides calories have a significant impact on body fatness. It may end up being true that macronutrients impact body fatness independently of calories in certain specific scenarios, for example people trying to maintain fat loss. But that's all speculation for the time being-- the evidence isn't there yet.

Tom Jeanne said...

Hi Stephan,

Haven't had time to follow your blog much lately (which is very sad!) but I am curious what your take is on this commentary in Nature. The authors seem to be saying that consumption of processed foods low in protein is a chief cause of obesity, then they turn around to say, well, nutrition is complicated and "requires a more integrated view of nutrition than is offered by the hegemony of the calorie or the search for a single culprit". This seems rather contradictory to me. Nevertheless, the idea of cheap low-protein foods contributing to obesity does not seem implausible.

Pauly said...

I realize i'm quite late to this "party", but i've recently acquired a taste for this debate. As I work in the gut microbiome field, everyone takes it for granted that the microbial composition of your gut is crucial to how you process food. Thus, calorie intake is only one component that drives obesity.
Personally, i find this to be a load of crock. Sure, there's probably some marginal impact of the microbiome on the energy you extract from your food, but "marginal" is the work to focus on.
However, i'm having a hard time finding enough data to "prove" that calorie intake is the most important variable in the model. 5 points do not even make it close. Does anyone know of a resource which would have a more extensive dataset on this?