Doctor, what diet should I try?

Several years ago, Gary Taubes published an article in the New York Times (“What if It’s All Been a Big Fat Lie”) in which he accused the American medical establishment of being “the cause of the rampaging epidemic of obesity in America.” Ouch. Mr. Taubes contended our typical “eat less fat and more carbohydrates” advice is dead wrong and the reason why we are all so fat. He blamed us for creating the obesity epidemic. I have to admit, I have read a lot of papers on proper diet over the years and it is easy to be confused on the best advice for our patients. I have spent 36 years telling my patients to eat less and exercise more. This is the same advice I have given myself for most of my own life with marginal results. Do we really know what works?

Americans get a lot of advice and spend a lot of money trying to lose weight. Weight loss books doubled in sales in the mid 2000’s. Weight loss books are often reviewed and endorsed by celebrities such as Oprah Winfrey and celebrity dieters may receive $500,000 to $3 million dollars to endorse a popular diet (this works out to about $33,000 per pound lost by a celebrity diet endorser). The 108 million Americans on a diet in any given year spend over $30 billion dollars per year on diets, diet books, weight loss medications, and bariatric surgery.

Traditional diet recommendations suggest a low fat, calorie restricted diet high in complex carbohydrates (Weight Watchers). A variant of that diet is the very low fat diet (Ornish). The low carbohydrate diets (Atkins, South Beach, Paleoliothic) promise more rapid weight loss without calorie restrictions. Low glycemic diets (Sugar Busters, Zone, Nutrisystem) restrict many carbohydrates and also avoid saturated and trans fats. I was particularly distressed to review the Blood Type diet since with my type A blood, I am restricted to a 1200 calorie vegetarian diet (Lord, take me now).

There have been several head to head studies on these diets. Most studies are 12 months or less. What have we learned? In general, low carbohydrate diets helped people lose more weight by 6 months, and were slightly better but not statistically significant than low fat diets at 12 months (5 kg lost for low carbs and 3 kg lost for low fat). RCTs have not shown significant differences between Atkins, Ornish, Weight Watchers, and Zone diets. There were more differences between patients in each group than between the types of diet studied, so tailoring diet recommendations to your patient’s individual situation makes sense – patients with high insulin resistance have been shown to respond better to low glycemic diets. None of the diets studied adversely affected serum lipid levels and all lowered A1c levels. However, long term studies on these diets have not been done, so overall effects on cardiovascular markers or overall mortality are not known. In the few longer term diet studies that have been done, adding exercise to diet improved weight loss outcomes at 36 months, but cardiovascular end-points were similar between diet alone or exercise alone groups.

My advice: support any diet your patient will follow long term. You may want to encourage a low glycemic index diet for your patients with metabolic syndrome. It is still OK to recommend fruits and vegetables regardless of diet choice. Exercise augments weight loss and we should encourage daily exercise as a way to maintain weight loss regardless of the diet your patient chooses.

Jim Cotter, MD

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