Low-Carb vs. Low-Fat Diet for Diabetics

David Mendosa Health Guide December 06, 2007
  • Almost everything that we thought we knew about fat is wrong.

    The “really bad fats,” according to Barry Sears of The Zone fame, are saturated fats, trans fats, and arachidonic acid. He says that the polyunsaturated fat known as arachidonic acid “may be the most dangerous fat known when consumed in excess.”

    Everyone seems to agree that trans fats really are bad for us. But new research shows that the saturated fat and arachidonic acid that we eat can actually be a good thing.

    But it depends. Specifically it depends on whether we are following a low-carb or a low-fat diet.

    Most health authorities, including the American Diabetes Association, still recommend low-fat diets. This is the legacy of Ancel Keys, a doctor who was all too persuasive for our own good. He persuaded the American medical establishment that fat is bad and carbs are good when those experts bought into his analysis of the “Seven Countries Study.” That study seemed to show a strong association between cardiovascular disease and intake of saturated fatty acids.

    It didn’t. One of the great strengths of the new book, Good Calories, Bad Calories by Gary Taubes, is how thoroughly he exposes the flimsy evidence linking dietary fat with heart problems. The emperor, Keys, figuratively wore no clothes.

    But when we follow a low-carb diet – meaning that we correspondingly increase how much fat we eat – something paradoxical happens. “You can actually eat more saturated fat and see a reduction in saturated fat in your plasma,” says Jeff S. Volek, PhD, RD, associate professor of kinesiology at the University of Connecticut.

    Dr. Volek is the lead researcher of a forthcoming study, “Comparison of Low Fat and Low Carbohydrate Diets on Circulating Fatty Acid Composition and Markers of Inflammation,” in the journal Lipids. The journal thought the results were so important that it published it electronically ahead of print and an abstract is free online. Dr. Volek kindly sent me a copy of the entire article and responded to my questions in a follow-up telephone interview.

    Most people find this inverse relationship between dietary fat and the fat in our blood to be counterintuitive. I certainly did before I began my study of fat metabolism.

    “This clearly shows the limitations of the idea that you are what you eat,” Dr. Volek says. “Metabolism plays a big role. You are what your body does with what you eat.”

    Dr. Volek and his associates studied 40 overweight men and women for 12 weeks. They compared the results of the two groups on a very low-carb diet (35 grams of net carbs and 100 grams of fat, including 36 saturated grams) with a low-fat diet (191 grams of net carbs and 24 grams of fat, including 12 saturated grams). Both groups ate about 1500 calories per day.

    Despite the three-fold greater saturated fat in the diet for the low carb group, saturated fat in the blood turned out to be higher in the low fat group. This is due to the process known as carbohydrate-induced lipogenesis, which I just wrote about here at “Eat Fat, Grow Thin.”

  • “That’s exactly right,” Dr. Volek told me. “The main connection is with insulin. You can’t ignore the carbohydrate-insulin axis. It’s basic metabolism. You are taught in your elementary biochemistry that insulin is an anabolic hormone and it stimulates anabolic factors. So it promotes lipogenesis through a variety of transcription factors and at the same time inhibits lipid oxidation too, the lipase. No one argues that.”

    But that’s as far as people have gone with it. Until now.

    “Where people don’t make the connection is that diet can actually impact that hormone, and that affects some of these outcomes that we are looking at,” Dr. Volek continued. “It is really showing carbohydrate as a control element of metabolism and its effects on insulin.”

    They found that the very low-carb diet had a greater anti-inflammatory effect. It significantly reduced a couple of markers, particularly palmitoleic acid (16:1n-7), which is a well accepted surrogate for lipogenesis. That and the increased fat activation are the mechanisms, Dr. Volek says.

    It must be hard for the establishment to swallow the saturated fat story. But it is probably throwing up on the new arachadonic acid research.

    The arachadonic acid results of the new research that Dr. Volek led are just as surprising as what they learned about saturated fat. People on the very low-carb diet showed substantially greater increase in arachidonic acid that scientists have commonly viewed as contributing to inflammation. But at the same time many of the inflammatory markers significantly decreased.

    How is this possible?

    “There has been this negative view of arachadonic acid, primarily because people have focused on its products rather than the intact fatty acid itself,” Dr. Volek told me. “It is indeed the source of a lot of proinflammatory ecosanoids that promote inflammation and thrombosis and so forth, but that is only if it is acted upon by the oxygenators or if it comes in contact with molecular oxygen.”

    On a low-carb diet the difference is that we have less oxidative stress. So the arachadonic acid doesn’t degrade. Its proportion in the membranes actually increases. In fact, the higher the arachadonic acid went up the less the inflammation, Dr. Volek told me.

     “That is a totally new concept,” he says. “There are a lot of misunderstandings and over-generalizations about arachadonic acid. We actually need to view arachadonic acid as a positive thing. It contributes to fluidity in membranes.”

    I couldn’t resist asking Dr. Volek a personal question. “Do you follow a low-carb diet yourself?” I asked.

    “I do,” he replied. “I am happy to say that I am not a hypocrite.”

    He says that he has followed this diet for about 20 years because on it he feels better. His diet is 10 to 15 percent carbohydrate, probably around 50 grams a day. It’s a bit more grams than the very low-carb diet in his recent study, because he doesn’t have a weight problem.

  • Dr. Volek has also been writing about low-carb diets for years, trying to get the word out. A MEDLINE search of peer-reviewed literature shows that he has authored or co-authored 146 protessional papers, many of them on low-carb diets.

    I asked him what comes next in his research. He says that he will study qualitative factors.

    I told Dr. Volek that as I switched to a higher fat diet I am finding that the fats that I really like are cream cheeses and stuff like that, which are pure fat. I wonder whether it matters what the source of the fat is?

    “That is a really good question,” he replied. “We have trials right now in progress where we are specifically asking that question. That hasn’t been addressed formally in any studies, and it is hard to guess what is going to happen. Certainly under normal carbohydrate intake you can make the case that the type of fat matters, but when you titrate carbs down pretty low and insulin is low, it may not be as important. So give us about 6 months and we will have some answers on that question.”

    I also wondered about advanced glycation end-products (AGEs). Are they as important a consideration on a low-carb diet as they clearly are on the standard high carb diet?

    Dr. Volek says that A1C, which does go down when people follow a low-carb diet, is the only AGE marker that low-carb trials have measured. “But it is something that definitely needs to be pursued and documented.”

    I will, of course, pursue Dr. Volek and his further research and report his further findings here. Be prepared for even more paradoxes in this important and fascinating story of fat metabolism.