It seems that every few a months a new diet hits the market claiming to be easier than its predecessors and to lead to more weight loss. Many of these diets call for reductions in calories, often through lowering carbohydrates, fats or both. Studies have gone back and forth about whether one is more helpful than the other, when it comes to both weight loss and overall health. Proponents of the low-fat lifestyle have claimed that diets high in fat increase cholesterol intake and could lead to heart disease. Those on the low-carb side pointed to conflicting evidence about the association between dietary fat and heart disease and the prominent role carbohydrates have played in the obesity epidemic.
A new study out this week hoped to find an answer among these conflicting viewpoints. Researchers took a group of 150 participants from a variety of backgrounds and randomly put them into a group that was instructed to reduce either carbohydrate intake or fat intake. Importantly, no calorie restrictions were put on either group, meaning they could eat as much as they wanted. The goal was to cut carbs or fat, not count calories. The researchers watched the participants for a year and then compared several health measures in the two groups.
Participants in the low-carb diet were asked to eat mostly protein and fat, with fat intake focused mostly on unsaturated fats that come from nuts, plant oils and fish. They were told to aim for 40% of their calories coming from fat sources. The low-fat group was asked to reduce their fat intake so that it made up less than 30% of their daily calories. Both groups were encouraged to eat fruits and vegetables.
While both groups lost weight at the end of the year, the low-carb group lost eight pounds more on average. Importantly, the low-fat group lost weight more often in the form of muscle as opposed to fat, the opposite of what was desired. Low-carb eaters on the other hand, actually saw improvements in lean muscle mass in spite of the fact that exercise wasn’t part of the required diet.
Additionally, those in the low-carb group saw dramatic changes in their blood measures. Markers of inflammation decreased, as did their triglycerides, which is a type of fat the body circulates in the blood. Their “good cholesterol,” or HDL, also rose dramatically. Blood pressure, total cholesterol and LDL (“bad cholesterol”) all remained the same in both groups.
All these positive changes in the low-carb group added up. When the benefits were totaled, low-carb eaters had reduced their risk of heart disease as measured by the widely used Framingham Risk Score. Those in the low-fat group saw some benefits but not enough to budge their cardiac risk.
While the study is by no means the final word on the benefits of low-carb versus low-fat diets, it provides strong evidence that the way we think about fats and sugars in our diets may be out of whack. Significant focus has been placed on removing fats from our diets, but this study shows that it may be more important and beneficial to our overall health to be watching carbs, regardless of how much we eat overall.