Early in 2013, US News & World Report asked a panel of 22 diet experts to rank 28 popular diets. The criteria: Were they effective for short-term or long-term weight reduction? Were they easy to follow? Were they safe and nutritionally balanced?
Topping the list was the DASH diet. (A variation of DASH called OmniHeart is the diet recommended by most health experts.)
Dead last? The Paleo diet, which the panel noted was supported by studies that were “few, small, and short.”
Loren Cordain, an exercise physiologist at Colorado State University and author of The Paleo Answer: 7 Days to Lose Weight, Feel Great, Stay Young, disputed the panel’s conclusions.
“Five studies, including four since 2007, have tested ancestral—or Paleo—diets and have found them superior to Mediterranean diets, diabetic diets and typical Western diets in regards to weight loss, cardiovascular disease risk factors, and risk factors for type 2 diabetes,” he wrote to the magazine.
But all five studies cited by Cordain were just as US News said: small and short term. Three of the five didn’t compare people who were randomly assigned to either the Paleo diet or another diet. Without that “control group” following another diet, researchers couldn’t tell if people lost weight because they were on a particular diet or simply because they were participating in a study.
In one of the two studies that did compare Paleo with other diets, Swedish researchers randomly assigned 29 middle-aged or older men with heart disease and pre-diabetes or type 2 diabetes to an “Old Stone Age” diet (lean meat, fish, fruits, vegetables, root vegetables, eggs, nuts) or to a “Mediterranean” diet (whole grains, low-fat dairy foods, vegetables, fruits, fish, oils, margarine).
After 12 weeks, the Paleo eaters had lost no more weight than those on the Mediterranean diet. However, the Paleo group did have lower blood sugar levels after a glucose tolerance test, which measures how well insulin controls blood sugar.
Two years later, the same researchers looked at 13 men and women in their 60s with type 2 diabetes. The volunteers were told to eat a Paleo diet for three months and then a standard diet for people with diabetes for three months, or vice versa. The Paleo diet had more fruits, vegetables, lean meat, fish, nuts, and eggs, and no grains, dairy, beans, refined fats, sugar, candy, soft drinks, or beer.
They ended up eating 300 fewer calories a day on the Paleo diet, which may explain why they lost seven more pounds during those three months. And their triglycerides were lower. But there were no differences in blood sugar levels after a glucose tolerance test.
The bigger question: What happens over the long run? At least three trials have compared diets that were either high or low in protein, carbohydrates, or fat—such as Atkins, Ornish, Weight Watchers, and The Zone—on a total of more than 1,200 people.
After one or two years, none of the diets outshined the others. What mattered most was whether people stuck to them. (The more extreme diets—like the high-protein Atkins and the low-fat Ornish—were the hardest to stay on.)
The bottom line: There’s no good evidence that the Paleo diet will make those extra pounds vanish.
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