A study was reported a month ago that looked at the correlations between people’s diet and weight gain. The key findings were reported as:
Within each 4-year period, participants gained an average of 3.35 lb (5th to 95th percentile, −4.1 to 12.4). On the basis of increased daily servings of individual dietary components, 4-year weight change was most strongly associated with the intake of potato chips (1.69 lb), potatoes (1.28 lb), sugar-sweetened beverages (1.00 lb), unprocessed red meats (0.95 lb), and processed meats (0.93 lb) and was inversely associated with the intake of vegetables (−0.22 lb), whole grains (−0.37 lb), fruits (−0.49 lb), nuts (−0.57 lb), and yogurt (−0.82 lb) (P≤0.005 for each comparison). Aggregate dietary changes were associated with substantial differences in weight change (3.93 lb across quintiles of dietary change). Other lifestyle factors were also independently associated with weight change (P<0.001), including physical activity (−1.76 lb across quintiles); alcohol use (0.41 lb per drink per day), smoking (new quitters, 5.17 lb; former smokers, 0.14 lb), sleep (more weight gain with <6 or >8 hours of sleep), and television watching (0.31 lb per hour per day).
Unsurprisingly this had been picked up by a lot of the media with headlines screaming Potatoes Make You Fat. While eating potato crisps and hot chips is associated with weight gain hasn’t surprised many, the fact that potato in any form is strongly correlated to weight gain seems to the big surprise. From the Washington Post
Every additional serving of potatoes people added to their regular diet each day made them gain about a pound over four years.
Although the study did not evaluate why potatoes would be particularly fattening, other research shows that starches and refined carbohydrates such as potatoes cause blood sugar and insulin to surge, which makes people feel less satisfied and eat more as a result, Mozaffarian said.
As an observational study, it is problematic to try and draw conclusions. Are potatoes inherently fattening, or do people who eat a lot of them unhealthy with their whole lives. Are whole grains correlated with lower weight-gain because they are objectively healthier, or because people who eat them are particularly health conscious. The same question could be asked for why yoghurt is apparently the dieters friend. The lifestyle factors also raise questions:
Lifestyle factors were clearly important. Those who exercised more gained nearly 2 pounds less than those who increased their physical activity the least. People who slept less than six hours a night — or more than eight hours — were more likely to gain weight, possibly by unbalancing hunger hormones such as ghrelin. Every extra hour per day of television watching added about a third of a pound, perhaps by encouraging snacking.