Friday, July 22, 2011

Insight into the Obesity Epidemic

My sister forwarded me an excellent article from the New York Times on new research published in the New England Journal of Medicine. As I do in these instances, I accesssed the original research instead of taking the journalists word for it. Anyone interested in obesity and weight management and how lifestyle choices impact the course of weight gain over our life should read this.

What the authors did is look at the lifestyle choices over time of the individuals in three massive cohort studies (the Nurses Health Study, the Nurses Health Study II, and the Health Professionals Follow-Up Study). In total this included 98320 women and 22557 men. When all was said and done they had amassed 1.6 million person-years of followup. That is a lot of followup in case you're wondering. What they were looking for was which lifestyle factors were associated with weight gain over the study period. They wanted to know which ones were positively associated (if you do more of that thing you increase your rate of weight gain) and which were inversely associated (the less you do of that thing the faster you gain weight or the more you do of it the slower you gain weight).

The average weight gain across all three cohorts was 3.35lb per 4-year period, equating to 16.8 lb over a 20-year period. This about fits with the traditional knowledge that weight gain is not sudden but instead very sneaky, with the average person gaining 0.5-1 lb per year during their adult life. The really interesting stuff I highlight below. Enjoy.

1. Almost EVERY dietary factor was independently related to weight change, either up or down.
2. Dietary factors with largest positive associations with weight gain were, in descending order:
-potato chips
-sugar-sweetened beverages
-unprocessed red meats
-processed meats
3. The weight gain associated with increased potato consumption was due mostly to increased french fry consumption. In fact, FRENCH FRIES, OF ALL THE FOODS STUDIED, HAD THE STRONGEST POSITIVE ASSOCIATION WITH WEIGHT GAIN.
4. Weight gain associated with increased consumption of refined grains was similar to that for sweets and desserts.
5. Inverse associations (consumption of food goes up, weight gain goes down) with dietary patterns and weight gain were found for increased consumption of:
-whole grains
-in descending order, meaning that the more yogurt one ate, the less their weight changed, even more so than with vegetables; weird.
6. Lifestyle changes aside from diet had more modest impacts on weight change
7. Interestingly, ABSOLUTE levels of physical activity, rather than the changes in activity a person was doing, were not associated with weight change. Makes sense but goes against common wisdom. It doesn't matter how much exercise you do because you have adjusted your caloric intake to match it. What matters is if you start doing significantly more or less exercise.
8. Thanks Captain Obvious: Increases in alcohol use were associated with weight gain. Wow.
9. The sweet spot for sleep was 6-8 hours per night. More weight gain was seen with less than 6 OR more than 8 hours of sleep a night.
10. The impact of lifestyle changes did not seem to change depending on ones age or starting weight or BMI. Interesting. Never too late to change I guess.
11. I love this part so I'll just quote it verbatim:
"Some foods---vegetables, nuts, fruits, and whole grains--were associated with less weight gain when consumption was actually increased. Obviously, such foods contain calories and cannot violate thermodynamic laws. Their inverse associations with weight gain suggest that the increase in their consumption reduced the intake of other foods to a greater (caloric) extent, decreasing the overall amount of energy consumed. Higher fiber content and slower digestion of these foods would augment satiety, and their increased consumption would also displace other, more highly processed foods in the diet."
12. They are totally baffled by the finding that yogurt had one of the strongest inverse associations with weight gain. The authors suggest that the finding is likely confounded by some factor not accounted for by their study methods. That is, those who change their yogurt consumption habits have other weight-influencing behaviors that weren't caught by the study.
13. The study found that increased consumption of almost ALL liquids, with the exception of water and dairy, was positively associated with weight gain.
14. Dairy was neutral. Too bad for the dairy lobby.
15. The traditional "wisdom" on diet did not stand up in this study. That is, calories matter, but are not everything. In fact the quality of the diet seems to determine the quantity of calories consumed, not vice versa. Fat doesn't seem to make a hell of a lot of difference (no differences between whole milk and low-fat milk, nuts inversely associated with weight gain even though they're incredibly high in fat). High energy density foods aren't always bad (nuts are very high energy density, low density beverages were associated with weight gain). And refined carbohydrates caused weight gain regardless of whether the sugar is added (sweets and desserts) or not (refined grains).
16. Between 1971 and 2004, the average dietary intake of calories in the US increased by 22% for women and 10% for men, mostly due to increased intake of refined carbs, starches, and sugar sweetened beverages.
17. A habitual energy imbalance of 50-100 calories per day is sufficient to cause weight gain in most individuals. This means unintended weight gain occurs easily but, conversely, that modest, sustained changes in lifestyle can mitigate or reverse this imbalance.
18. Not once did they mention in the article that any of these things were associated with weight loss. ALL of the cohorts gained weight over the study period. It did not in fact say that if you eat more fruits and vegetables you'll lose weight, you'll just gain LESS over time than you would have otherwise. We'll see what the media does with this one.


Mozaffarian D, Hao T, Rimm EB, Willett WC, Hu FB. Changes in Diet and Lifestyle and Long-Term Weight Gain in Women and Men. N Engl J Med 2011;364:2392-404.