Are low fat diets the best option for sustained weight loss?

The Study
Some of the most accomplished professors at Harvard University’s Department of Nutrition conducted a systematic review of weight loss trials to determine if low fat diets increased rate of weight loss compared to other approaches. After comprehensively evaluating the literature, 53 studies were identified that included over 68,000 participants. The findings were very interesting:

-In weight loss trials, low carbohydrate interventions led to significantly greater weight loss than low fat interventions (a difference of about 2.5 lbs.).

-Low fat diets did not lead to a difference in weight change when compared to higher fat weight loss approaches.

-In weight loss trials, higher fat diets led to significantly greater weight loss than low fat diets when groups differed by more than 5% of calories obtained from fat at follow-up (a difference of about 2.5 lbs). The Lancet 2015; 12:968-79.

Take Home Message

Despite decades of advice to the contrary, low fat diets really are not the best strategy for weight loss. There are a few reasons why dieters struggle with a low fat approach:

1) Since protein tends to stay relatively constant in most dieters, when they decrease fat, they increase carbohydrate consumption. In the American diet, this usually means more refined carbohydrates. Since fat acts to stabilize the blood sugar, the low fat, high carbohydrate pattern of eating causes a reactive hypoglycemia in many people that leaves them hungry. Over time, this hunger wins out and the dieter ends up snacking and overeating.

2) These swings in blood sugar also promote higher than normal insulin levels. There is evidence that higher insulin levels promote fat storage through a variety of mechanisms. 

Therefore, for many who attempt a low fat approach to weight loss, they are hungry, eating more, and storing fat at a higher rate. Not a good combination!

While there are certainly people that will do very well on a low fat diet, the research shows that for the typical person trying to lose weight, there are better options.

In both my analysis of the literature and my clinical practice, I have found the Mediterranean approach to be much more effective. This is a moderate fat, moderate carb, low glycemic load diet that stabilizes blood sugar and dramatically decreases hunger. My clients do amazingly well with this approach to weight loss.