Low-fat diets peaked in popularity about 25 years ago, and low-carb diets 10 years ago. Neither turned out to be the magic bullet for long-term weight loss. Still, the two diets keep slugging it out in studies, and low-carb seems to be winning more rounds.
The latest study, published in the Annals of Internal Medicine in September 2014, involved 148 middle-aged obese people who had no history of cardiovascular disease, diabetes, or kidney disease. For a year they followed either a moderately low-carb diet (similar to the maintenance phase of the Atkins diet) or a modestly low-fat diet (similar to American Heart Association guidelines).
Participants received individual and group counseling, including sample menus and recipes, but no specific calorie goals. They did not change their exercise habits.
Here are some key findings:
- After a year, average weight loss was about 12 pounds for the low-carb group and 4 pounds for the low-fat group. Those are small losses for people who weighed 210 pounds on average, especially in light of the fact that they reported cutting their daily calorie intake by 500 to 750 calories a day for a year. The low-carb diet led to greater calorie reduction, so of course it resulted in greater weight loss.
- The low-carb group changed their diet much more than the low-fat group did. They cut the proportion of carbs in their diet dramatically, while the low-fat group cut their proportion of dietary fat only modestly (to just under 30 percent of daily calories, which is not very low for fat).
- Unlike the low-fat group, people on the low-carb diet saw their HDL (“good”) cholesterol rise and triglycerides drop, and their estimated 10-year risk of heart disease improved—not surprising, since they lost more weight. LDL (“bad”) cholesterol did not change in either group.
But there are some lingering questions: What would have happened if the study had continued? Would participants have done as well if they had not been given fairly intensive counseling? Would the low-fat diet have been more effective if it required people to make bigger changes in the way they ate? How would the diets affect the risk of heart attacks and strokes, as well as kidney disease, cancer, and bone density? And would low-carb diets be safe and effective in people who have cardiovascular or kidney disease (they were excluded from this study)? No one knows.
A bigger picture
A week after this study came out, an analysis of 48 studies of popular diets (including Atkins, Zone, Weight Watchers, Jenny Craig, Ornish, and South Beach) was published in the Journal of the American Medical Association. It found that all diets—low-fat, low-carb, or somewhere in between—were at least minimally effective, with little difference in weight loss from one plan to another, provided people stuck to them.
One size doesn’t fit all
Find a way of eating that works best for you, something you can stick to for years, since keeping off the lost pounds is the hardest part. Some people do better by cutting carbs, others by cutting fat—and by eating more protein. Whatever the fat/carb/protein ratio of your diet, opt for “good” carbs (in vegetables, fruits, beans, whole grains), “good” fats (in fish, nuts, seeds, vegetable oils), and lean protein. And don’t forget this key to long-term success—exercise.