It seems like every other week there is some new study out that “proves” one way or the other that low-carb is king or low-fat is best. Part of this is journalists looking for an easy story–read (or skim) a 16 page article, get a quote, write it up. There is always a new study when the news cycle moves on.
The new study this time is out of Tulane University and published in the Annals of Internal Medicine (this is serious stuff) and says that eating a low-carb diet is good for you–or at least better for you than low-fat diet. I saw an article about it in the local paper, and looked it up later to find something about it in the New York Times.
Now, everyone seems to have an opinion, so I thought I’d try to break it down. First, though, I have a bias, and you should know what it is. I think that saturated fats can be a very healthy part of your diet, that the type of unsaturated fat is very important, and that synthetic trans-fats should not pass your lips if you can help it. Whole grains and legumes are good, vegetables are great. I also think dairy–for those who can eat it–can be a valuable part of your diet.
So, for the actual study. This was a study of 119 individuals without heart disease and diabetes. The study was done to measure the effectiveness of a low-carb diet for weight loss. Researchers found that a low-carb diet did indeed work better for weight loss than the low-fat diet; it even improved cardiovascular risk factors.
So, what did the diets look like? Since participants were not asked to count calories, the low-fat group was instructed to limit their fat intake to 30% of daily calorie intake and the low-carb group was restricted to 30 grams of carbohydrates per day. For a 2000 calorie per day diet, 30 carbs is about 10% of the recommended daily value. The low-fat group is actually eating the recommended daily allowance of fat based on the FDA Guidelines*. Both groups were advised to limit saturated fats and choose unsaturated fats. Additionally, participants from both groups meet with dietitians throughout the study, both one-on-one and in small groups.
Now, for those of you who have been following along on my articles on research and studies, you will remember the importance of the type of study. This was a randomized trial, so we can draw conclusions from this test. With only 119 people in the study, it is s definitely on the small side, so I won’t extrapolate too much from it.
Since participants maintained a level of physical activity through the study, this lend credibility to the weight loss being due to diet. Those in the low-carb group lost weight faster (through the first 6 months) but ultimately the low-fat group caught up by the end of the year. The changed in cardiovascular risk factors was also likely diet induced. In the low-carb group, HDL increased and the ratio of total cholesterol to HDL decreased. Additionally, participants in this group reduced their risk of getting heart disease, whereas the participants in the low-fat group did not.
For any future medical professionals out there, this study is important because it demonstrated that a low-carb diet was effective for improving risk factors for heart disease and for dropping weight. As the authors say,
Because CVD is the most common cause of death in the United States and obesity is a particularly prevalent risk factor, our study has important clinical and public health implications. Findings from this trial may offer new evidence for the recommendation of a low-carbohydrate diet to obese persons as an additional nonpharmacologic approach for weight loss and reduction of CVD risk factors.
I’d love to see another study like this that doesn’t demonize healthy sources of saturated fats and takes care to emphasize a healthy ratio of polyunsaturated fats. But all in all, this study was interesting and it is great to know that there are novel ways to treat or prevent chronic disease with diet.
Bazzano, Lydia A, Tian Hu, Kristi Reynolds, Lu Yao, Calynn Bunol, Yanxi Liu, Chung-Shiuan Chen, Michael J Klag, Paul K Whelton, and Jiang He. 2014. “Effects of low-carbohydrate and low-fat diets: a randomized trial.” Annals Of Internal Medicine 161, no. 5: 309-318. MEDLINE with Full Text, EBSCOhost (accessed September 4, 2014).
*So, this 30% of your diet is made up of fat thing sounds pretty high, right? It’s not that high. Most dietary guidelines recommend getting between 25 and 35% of your energy from fat–including the CDC. Getting 20% or less of your energy from fat is a very low-fat diet. Besides–America is the land of low-fat; our government and universities and Ansel Keys have been trying to make us eat low-fat since forever. I would say that the Nutritional Guidelines are what could be considered low-fat (or lower-fat), given it is kind of an American Healthcare obsession. By the by, you may be interested to know that some of the countries with the least heart disease-related deaths per capita eat more fat (and have a higher ratio of saturated to polyunsaturated fats) than is recommended? For instance, the French and the Greeks (ever heard of the heart-healthy Mediterranean diet? It is an import from Crete in Greece).