I thought this Wall Street Journal article about the JAMA study on Body Mass Index (BMI), Is Being Overweight Healthy?, was interesting though it didn’t address the reasons why higher BMI might be protective (as discussed in my original post).
“For instance, according to his BMI, one numbers-savvy researcher is overweight—a finding he rejects. “As a 6’3″ swimmer, I find myself falling in the lower part of the overweight category even though my body-fat percentage is very low and no one would say I was overweight,” said David Dunson, a biostatistician at Duke University. He said he knows athletes who lose muscle, not fat, when they fall off their exercise regimen, and then are counterintuitively reclassified from overweight to normal weight.
“It is hard to say how many people are misclassified by BMI. Steven Heymsfield, executive director of the Pennington Biomedical Research Center, an NIH-funded institution in Baton Rouge, La., who co-wrote a commentary accompanying the JAMA study, estimated about 5% to 10% of the U.S. population may be ill-served by BMI.”
“The perspective that is gaining support is one that points away from the scale, and toward healthy habits that are sustainable—that is, habits that not only support health, but that also don’t leave you feeling hungry and deprived.”
You might have heard about the meta-analysis released January 2 in the Journal of the American Medical Association, Association of All-Cause Mortality with Overweight and Obesity (1), which found that “overweight” people, based on body mass index (BMI) had a lower risk of mortality than what is considered a healthy BMI.
Before I had a chance to read the study myself, I came across a USA Today article, Experts weigh in on the dangers of extra pounds, quoting the well-respected nutritionist, Dr. Walter Willett from Harvard School of Public Health, about the JAMA study:
“The most serious problem in the paper is that the normal-weight group included a mix of lean and active people, heavy smokers, patients with cancer (and) other conditions that cause weight loss, and frail elderly people who had lost weight due to rapidly declining health. Because the overweight and obese groups were compared to this mix of healthy and ill persons who have a very high risk of death, this led to the false conclusions that being overweight is beneficial and that grade 1 (moderate) obesity carries no extra risk. The new statistics are completely misleading for anyone interested in knowing about their optimal weight. … The paper is a pile of rubbish.”
Yikes! That’s quite a rip on the JAMA study’s authors. Not only that, but why would a research group put so much effort into a meta-analysis but fail to adjust for some of these obvious confounders, and why would JAMA publish it?! But Willett’s criticisms would explain how they could have reached such a counter-intuitive finding and all would still be good in the nutrition universe.
I read the study fully intending to find the criticisms by Dr. Willett to be valid. Alas, I did not. From my reading of the paper, they did adjust for smoking and age, and analyzed the study for any bias due to “frail elderly people.” They did some testing to make sure previous heart disease and cancer were not affecting the results.
The control groups for the studies in the meta-analyses were typically people with a BMI of from 18.5 to < 25 or from 20 to < 25. The study found that people with a BMI of 25 to < 30 had a statistically significant 8% reduced risk of mortality (.92, .88-.96). People with a BMI of 30 to < 35 had essentially the same risk of mortality. It wasn’t until you got to the group of people with a BMI of 35 or greater that risk of mortality significantly increased.
So, what could be going on here? Well, a BMI of 18.5 to 20 has often been considered to be unhealthfully thin, but from what I gleaned from the paper’s discussion, excluding such people did not appreciably affect the results.
BMI doesn’t account for muscle mass, as Willett alludes to above, but it is hard to believe that there were enough muscle-bound people in the meta-analysis to confound the results to any significant degree.
Willett went on to say in the interview:
“In the last several years, two other major analyses, involving the collaborative efforts of more than 150 scientists, have been conducted on the relation of body weight to mortality…these studies showed clearly that both overweight and all grades of obesity are associated with increased mortality.”
In contrast, the JAMA authors mention that their results are consistent with two previous meta-analyses. And they give some reasons why being overweight might be associated with lower risk of mortality:
“Possible explanations have included earlier presentation of heavier patients, greater likelihood of receiving optimal medical treatment, cardioprotective metabolic effects of increased body fat, and benefits of higher metabolic reserves.”
Occam’s razor would dictate that the best explanation is simply that it’s healthier to be “overweight,” and I don’t like doing backwards somersaults to wish away findings that, had they gone the intuitive way, would be unquestioned as solid. That said, given the prevalence of type 2 diabetes and the fact that vegans have been shown to have a much lower rate of type 2 diabetes and much lower average BMIs, I’m not going to try to gain weight. But it’s a little demoralizing to have one of the most basic ideas in nutrition ̵ that being overweight is not better than being a normal weight ̵ significantly questioned.
In conclusion: Rubbish? Not from what I can tell. Food for thought? Yes. As is often the case, this isn’t the last word.
Flegal KM, Kit BK, Orpana H, Graubard BI. Association of all-cause mortality
with overweight and obesity using standard body mass index categories: a
systematic review and meta-analysis. JAMA. 2013 Jan 2;309(1):71-82. | link
I read two studies from the May issue of the Journal of the Academy of Nutrition and Dietetics for continuing education credit. I normally don’t post about such studies, but these two were rather interesting.
Energy density is a way to measure food in calories per weight. Generally, this means that foods high in fiber and water are going to have lower energy density. A meta-analysis of 17 studies in adults and six studies in children found that low energy density foods were associated with lower fat mass and lead to improved weight loss and weight maintenance among both adults and children (1).
But when it comes to fiber intake, Americans barely increased their fiber intake from 1999 to 2008; it changed from 15.6 to 15.9 grams per day. The recommended amount of fiber for adults is 25 to 38 grams per day (or 14 grams per 1,000 calories consumed).
1. Pérez-Escamilla R, Obbagy JE, Altman JM, Essery EV, McGrane MM, Wong YP, Spahn JM, Williams CL. Dietary energy density and body weight in adults and children: a systematic review. J Acad Nutr Diet. 2012 May;112(5):671-84. | link
2. King DE, Mainous AG 3rd, Lambourne CA. Trends in dietary fiber intake in the United States, 1999-2008. J Acad Nutr Diet. 2012 May;112(5):642-8. Epub 2012 Apr 25. | link
“For the new study, researchers randomly assigned 100 obese 7- to 12-year-olds to one of three eating plans: one that followed the conventional wisdom of portion control; a low-carb diet; or a reduced glycemic load plan that cut down on certain carbs that typically cause surges in blood sugar…
“Over one year, all three plans worked equally well in controlling kids’ weight gain. The difference, researchers found, was that the low-carb plan was tough to stick with.
“…kids in all three diet groups ended up with healthier cholesterol levels.”
A study was published in the Journal of the American Dietetic Association’s August issue doing an analysis of protein and weight gain. The odd thing about it was that they used data from a cohort of male employees of the Chicago Western Electric Company — from the 1950s!
In any case, they found that, after 7 years of follow-up, animal protein intake was associated with being overweight and obese, but vegetable protein was the opposite — inversely associated with being overweight. This would be a no-brainer except that they found this independent of calories, fat, and carbohydrate. The findings were highly significant.
The researchers theorized that the different amino acid composition of the animal vs. vegetable protein could account for the difference.
It would have been interesting to see a cohort study done like this in which fat-free mass was included as a variable. In other words, did the people eating more animal protein have a higher muscle mass leading to a higher body mass index (the measure of overweight and obesity)? But even if it did, I’d be surprised if it could make up for the high level of statistical significance. Further research is needed!
Bujnowski D, Xun P, Daviglus ML, Van Horn L, He K, Stamler J. Longitudinal Association between Animal and Vegetable Protein Intake and Obesity among Men in the United States: The Chicago Western Electric Study. J Am Diet Assoc. 2011 Aug;111(8):1150-1155. (Abstract)
As someone who loves hearing good news about my bad habits, I was excited to read about Chris Voigt, the Executive Director of the Washington State Potato Commission, who is eating nothing but 20 potatoes per day for 60 days (link). Potatoes have been linked to diabetes and the theory is that it’s because of their high glycemic index (see here).
After 30 days Voigt’s health markers changed drastically:
Weight – 197 to 189 lbs
Total cholesterol – 214 to 162 mg/dl
HDL (good) – 45 to 46 mg/dl
Triglycerides – 135 to 100 mg/dl
Blood Glucose – 104 to 92 mg/dl
It only takes 11 potatoes to meet the RDA for all amino acids, and 13 to meet the RDA for protein (calculated using a white, baked potato and with a 10% buffer for vegetable protein).
It appears that he isn’t eating sweet potatoes or yams (especially since his vitamin A intake is very low), but I wasn’t able to verify that.
To be clear, I’m not recommending this diet.
Junk Food Diet
And here is another article, Twinkie diet helps nutrition professor lose 27 pounds, about Professor Mark Haub from Kansas State University. Professor Haub lost 27 lbs in two months of eating nothing but junk food. He says that this shows you can lose weight eating anything, as long as you eat less calories than you use.
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The study found that when people trying to lose weight slept 7.5 hours per night, they lost 3.1 pounds of fat and 3.3 pounds of fat-free body mass (mostly muscle tissue). When they slept for 5.5 hours a night, they only lost 1.3 pounds of fat and 5.3 pounds of fat-free mass.
A study from Taiwan published in April indicates that people who eat breakfast are more likely to be at a healthy weight. This reinforces most of the previous findings on the subject.
One theory as to why is that skipping breakfast leads to eating more calories later in the day, but that doesn’t seem to be the case as breakfast skippers have been shown in previous research to eat the same or less calories. It seems likely to me that skipping breakfast slows down your metabolism.
It also could be that skipping breakfast doesn’t cause the weight gain, but is merely associated with something else that causes it. To adjust for this possibility, the researchers controlled for age, gender, marital status, educational level, income, smoking status, alcohol consumption, and exercise, and so differences in these variables between breakfast skippers and eaters should not account for the differences in body weight.