People randomly assigned to either plan in the study lost weight at roughly the same pace and kept it off for roughly the same amount of time. At first glance, that finding seems to fly in the face of recent scientific wisdom on diet and health, which has begun to recommend welcoming fatty foods like butter and eggs back into our diets and curbing our intake of sugar and carbohydrates like rice and bread.
But not so fast.
In reality, the study did not compare a truly low-carb diet against a low-fat one. The people in the low-carb group were actually eating relatively high amounts of carbs —they were nowhere near the next-to-nothing carb counts that people on regimens like the keto diet achieve.
More importantly, all of the participants in the year-long study — regardless of which group they were in — were told to ramp up their intake of vegetables and slash their consumption of added sugars and refined grains,
The recent study was published last week in the Journal of the American Medical Association. The researchers randomly assigned 609 non-diabetic, overweight adults aged 18 to 50 to the low-fat or low-carb diet.
At the end of the study, people in both groups were found to have lost roughly the same amount of weight — about 29kg, 10kg of which they gained back within a few weeks after the study ended.
But precise rules regulating the quantities off carbs or fat the participants ate were only put in place for the first two weeks of the study, making it hard to measure actual quantities of carbs or fat consumed.
Plus, the participants were given other guidance on what to eat that could have played a large role in the outcomes the researchers observed.
All of the participants in the study were given two additional instructions on how to eat. First, they were told to "maximise vegetable intake" by eating lot more foods like bell peppers, kale, and greens — all of which have been linked to positive outcomes like weight loss and a reduced risk of disease.
Second, they were instructed to curb their intake of added sugars and refined flours — ingredients that studies have increasingly tied to a range of negative health outcomes including weight gain and diabetes. Beyond obvious carb-heavy items like bread and rice, sugar and carbs lurk in a range of seemingly healthy foods like salad dressings, yogurt, sauces, and supposedly "light" ice creams.
A growing body of evidence suggests that eating fewer refined carbs and more vegetables is helpful not just for losing weight and keeping it off, but also for reducing your risk of several major diseases including heart disease, diabetes, and some types of cancer.
Importantly, participants in both studies also ended up eating roughly the same amounts of protein each day. That's not surprising, given that protein-rich foods like eggs, fish, avocados, and beans fill us up and keep us full, making us less likely to over-indulge on such items.