Chapter summary
- Under 40, most people are already overweight, and slowly most become obese. Over 40, weight rises by about 0.5kg a year. Fewer than 30% remain a normal weight.
- The cause is what we eat, not our resolutions about diet and exercise.
- Without a change in food intake, you will gain about 1% of body weight a year. If you change what you eat, you can lose that weight.
- The middle-age spread is a slow process, shown in large studies of 120,000 to 300,000 people.
The Harvard study
Mozaffarian’s team (2011) analysed 120,877 non-obese women and men in three US cohorts, with checks every four years over 12 to 20 years.
- Overall: People gained 1.5kg (3.35 lb) every four years. Only 5% lost weight. Over 20 years the gain was 7.7kg (17.7 lb), about 0.6% a year.
- Foods linked to gain (per four years): French fries 1.5kg (the worst), crisps 0.8kg, potatoes 0.6kg, sugar-sweetened drinks 0.45kg, unprocessed red meat 0.4kg, processed meat 0.4kg, desserts and sweets 0.2kg, and fruit juice.
- Foods linked to less gain: vegetables, whole grains, fruit, nuts (0.3kg) and yoghurt (0.3kg).
- Diabetes: 6.5% developed type 2 diabetes. Swapping fruit juice for blueberries cut risk by 33%, grapes and raisins 19%, apples and pears 13%, any whole fruit 7%.
- Other factors: More activity meant less gain. One alcoholic drink a day added 0.2kg. Sleeping under six or over eight hours added weight. Each extra hour of TV a day added weight and snacking. New ex-smokers gained 2.3kg.
Where views differ
- “Eat less, exercise more”: Robert Lustig calls this naïve. Frank Hu of Harvard says people do better focusing on eating right rather than eating less.
- Calories do count: Marion Nestle agrees calories matter, but says it is easier to control them by eating healthfully and avoiding junk food than by counting.
- Why potatoes? Mozaffarian says maybe because of large portions, or because they spike blood sugar and insulin, making people hungrier.
- Why swap juice for fruit? Anthocyanins and polyphenols may help glucose uptake.
- Red meat: The study links it to some gain. The author is less worried about it than about refined carbohydrates.
- Limits: These are observational studies. They show correlation, not cause.
The take-out idea
- Take out TV time, sweet drinks and French fries.
- Diets that work best take something out, which can be easier than stopping everything at once.
References
- Mozaffarian, D. et al. (2011) Changes in diet and lifestyle and long-term weight gain in women and men. N Engl J Med 364:2392-2404.
- Malik, V. et al. (2010) Sugar-sweetened beverages, obesity, type 2 diabetes mellitus, and cardiovascular disease risk. Circulation 121(11):1356-64.
- Muraki, I. et al. (2013) Fruit consumption and risk of type 2 diabetes. BMJ 347:f5001.
- Ostrow, N. (2011) Potato chips cited as culprit in U.S. weight gain. Bloomberg.