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The recent study published in the Annals of internal Medicine titled “Effects of Low Carbohydrate and Low-Fat diets: A randomized trial” is sure to cause a lot of confusion. The headlines in the New York Times does not help. As always the devil is in the details, so it important to look at this study very carefully.
The study was designed to look at weight loss, blood pressure, blood sugar, and cholesterol levels at 3,6 and 12 months. It did not look at cardiovascular end points like heart attacks and strokes. There is much more to heart disease than cholesterol levels. The study defines low-fat as less than 30% of calories from fat so I am not surprised by the findings. The investigators compared a bad diet to a worse one; however, I am disappointed in the poor reporting by the Times.
The average total amount of fiber consumed at the start of the trial by both groups was 16 -18 grams and at the end of 12 months was around 15 grams. This falls short of the US dietary guidelines, which recommend 25 grams for women and 38 grams for men. If the low-fat group is getting only 15 grams of fiber, one can extrapolate that they are like most Americans, meaning they are most likely eating refined carbohydrates such as French fries, white bread, white rice, high fructose corn syrup, and other processed foods. If they were eating a diet rich in whole foods, their fiber content would be much higher.
The study reported no difference in blood pressure, LDL cholesterol, blood sugar level, and serum insulin level between both groups. It did find that the HDL level was higher in the low carb group. HDL plays a big role in preventing the arteries from getting clogged. High fat diets require a larger clean-up crew, so it is not surprising that the HDL level went up. Butter can increase your HDL for the same reason, but that does not mean that it is good for you. In fact, pharmaceutical studies have shown that when you artificially increase HDL levels mortality increases.
The triglycerides also went down in the low carb group. This is not surprising since this group reduced their intake of simple carbs by 1/2 from 234 grams to 127 grams in 12 months. Reducing refined carbohydrates will lead to a reduction in triglycerides. The total amount of calories consumed by the low carb group was less than the low-fat group at 3, 6, and 12 months, and it is therefore not surprising that they lost more weight. If the low carb group reduced both their simple carbs and fats, they would have lost more weight, but this was not studied.
There was no difference in LDL cholesterol, blood pressure, blood sugar and serum insulin levels in both groups. This is not surprising since they are both not great diets.
The cardiac (Framingham) risk score is calculated from age, sex, smoking, systolic blood pressure, total cholesterol, and HDL. Only total cholesterol and HDL were different between both groups and most likely accounts for the difference in the Framingham risk scores, which was higher in the low-fat group.
The title of the study is misleading when it refers to a low-fat diet. The study defines low-fat as less than 30% fat by calories. To me, that is not low-fat as it is close to the diet of the average American, which is approximately 35% fat. A more accurate title would call the study a comparison between a 30% fat diet and a 40% fat diet.
This is a comparison of the average American diet to a low carbohydrate diet. In essence this is a comparison of a bad diet to an even worse diet.
Foods high in carbohydrates are an important part of a healthy diet. The amount of carbohydrates is not as important as the type of carbohydrate. If we look at the Ornish trial, which used a plant-based, low fat (10%) diet, we would see a reduction of LDL cholesterol by 40% without medications and weight loss of around 22 pounds (10 kg) in 1 year. This diet, which is similar to the Esselstyn diet, may have high carbohydrates, but the carbohydrates included come from whole grains and vegetables not French fries, white rice and white bread.
In 2006, Drs. Berkow and Barnard reviewed 87 studies in a meta-analysis and concluded that vegetarian and vegan diets, in general , lead to greater weight loss than their meat counterparts.
Eating a whole foods low-fat (10 -15%) plant based diet has consistently been shown to be beneficial whether it is related to weight loss or disease prevention, and it would be interesting to see a future study compare it to a low carb diet.
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Bazzano A. L., Hu T., Reynolds K. et al, “ Effects of Low-Carbohydrate and Low-Fat Diets: A Randomized Trial.” Annals of Internal Medicine vol. 161, no. 5 (2014): 309–318.