As our last article explained, the recent Tulane University study on low-carb versus low-fat diets found an advantage in weight loss for the low-carb group. But let’s take a look at this study from a more long-term viewpoint. It’s one thing to eat a low-carb diet for a year and lose weight. But what happens if you eat this kind of diet for decades? Obviously we can’t do randomized trials on this. What we have to turn to for a decades-long view of diets is epidemiology. Epidemiology tells us that there is a wide range of human experience with true low-fat diets, but the same cannot be said for the low-carb diets that are being so highly promoted today. Long-time traditional diets of many countries are based on grains and vegetables, with very small amounts of meat, and a resulting fat percentage that would qualify them as low-fat. We often think of the Chinese or Japanese diets as being like this, but in actuality, many other populations have this type of diet as well. Before these populations began eating the Western diet, their health status was really quite good, with low rates of cancer and heart disease. As these populations adopted the Western diet, or moved to the United States or Europe, the incidence of cancer and heart disease began to rise to levels close to those of the United States. However, as we said earlier, there is very little human experience with what we refer to today as a low-carb diet, except possibly in Paleolithic times, and even this is open to debate. The only living population that exists on a high-meat, high-fat diet is the Inuit. Their diet, however, consists largely of whale and seal meat. Their health is generally good, though they experience an excess of hemorrhagic stroke, caused by overly thin blood. Further, they live an extremely different lifestyle from most of today’s low-carb followers.
Without significant experience with low-carb diets in today’s cultures, the most useful type of studies for exploring this question are cohort studies, in which large groups of people have been observed for decades while researchers recorded their diets, weights, disease incidence and other health parameters. Specifically, there are two studies from the US, with study groups consisting of doctors and nurses, respectively, which tracked diet and health outcomes for many years. These populations did include people who followed the equivalent of low-carb diets for long periods (remember, the low-carb diet has been with us for a long time, starting out as the Scarsdale Diet in the 1970s). Researchers were able to select these low-carb followers from the full populations, and tracked their health status. To do this, they developed a “low-carb diet score:” they divided the groups into 10 smaller groups, ranked from lowest to highest on fat consumption. Those in the top 10% for fat consumption got 10 points toward the score; the next 10% got 9 points and so on. Then they looked at protein consumption. The top 10% for protein consumption got another 10 points toward their low-carb score; the next 10% got 9 points. Finally, they looked at carbohydrate consumption. Instead of the top 10%, the lowest 10% got another 10 points added to their score; the next higher got 9 points, and so on up to the highest carb consumers, who got 0 points. The highest score a low-carb diet participant could get was 30.
Two studies using this scoring system have also added an interesting twist to the low-carb diet scores: they calculated similar scores for animal-based diets and plant-based diets, based on how much food from animal sources versus plant sources composed the low-carb diets. The first of these studies examined the risk of type 2 diabetes in study participants on low-carb diets. For low-carb diets in general, the risk of developing type 2 diabetes for those with the highest low-carb scores (30 points) was 10% less than those with the lowest, but this difference was not statistically significant. For participants with animal-based low-carb diets, the risk of developing diabetes was exactly the same as for those with the lowest low-carb diets. But participants following plant-based low-carb diets had an 18% lower risk of diabetes than those not following low-carb diets, which was statistically significant. The study also found that people with diets high in glycemic load had a much higher risk of diabetes than those with diets low in glycemic load. The second study looked at overall mortality for low-carb diets. In this case, the mortality for low-carb diet followers was 12% higher than those who did not follow low-carb diets, though this was not statistically significant. Those on animal-based low-carb diets did have a statistically significant 23% increase in overall mortality, as well as a 14% higher mortality from cardiovascular diseases, and a 28% higher cancer mortality, both statistically significant. Those on the plant-based low-carb diets had a significant 20% reduction in overall mortality and a significant 23% reduction in cardiovascular mortality, though no reduction in cancer mortality was seen. In contrast, consider that the most recent meta-analysis of low-fat diets finds that breast cancer patients who followed low-fat diets after diagnosis had a significant 23% reduction in breast cancer recurrence, as well as a significant 17% reduction in overall mortality. Early-stage prostate cancer patients assigned to a 10% fat diet experienced declines in PSA levels, whereas control patients on standard Western diets experienced increases. There are also numerous other studies illustrating the benefits of low-fat, plant-based diets on cancer survival, many of which Dr. Block reviewed in a chapter in an updated edition of the book Integrative Oncology, edited by Donald Abrams, MD, and Andrew Weil, MD, which was also published earlier this month.
The interesting message of these studies is that it appears that low-carb diets can result in weight loss, without immediate bad effects on cardiovascular disease parameters. However, to the extent that such diets rely mainly on meat, they do not appear to be associated with long-term improvements in mortality or cancer. Plant-based low-carb diets may be associated with improvements in mortality and cancer, but it’s not clear that these are truly relevant to cancer patients. We have particular concerns with some of the current plant-based low-carb diets, such as the Eco-Atkins diet, which relies mainly on highly processed wheat gluten and soy products as low-fat protein sources. What we believe will be much more likely to have good results with our patients is a modified version of the low-fat diet that emphasizes whole foods, truly whole grains, a high consumption of vegetables and fruits, and a variety of healthy, mostly plant-based protein sources, combined with exercise and prescriptive supplement use, and adapted to a patient’s specific nutritional status. Taking a page from what we believe low-carb diets do get right, we also believe that eliminating white sugar and refined flours as well as junk food is absolutely critical to good health.
If you have questions about our dietary recommendations, or to learn more about your specific nutritional needs, consider a consultation with one of the Block Center’s dietitians. For additional information, please call 847-492-3040.