Thursday, August 5, 2010

Lipids and Diet

Low-carb and low-fat diets result in similar weight loss at 2 years when both are accompanied by comprehensive lifestyle counseling, according to a recent research project by Gary Foster and colleagues published in the Annals of Internal Medicine.

But people in the low-carb diet showed better lipid profiles after 2 years.

You have to pay to read the full text of the article, but low-carb advocate Jimmy Moore has an extensive discussion of the results including some graphs.

This study is important because it shows that various improvements in people following low-carb diets are not simply temporary. Although 2 years can't really be called long term, it's heading in the right direction.

What I find fascinating is the reaction to this article. I can't find it at all on either Science Daily or Eurekalert, both popular summaries of science news. They're always quick to report studies that say red meat is bad or low-carb diets cause problems. Why aren't they summarizing this study? Many other media outlets are, so it's not that the study is obscure.

Others have put a positive or a negative spin or a neutral spin on the study (not mentioning the better lipid profiles is actually a negative spin), some by the way they write their headlines. If you support low-carb diets, you can emphasize the fact that the lipid levels improved on that diet. If you don't, you can focus on the fact that weight loss was the same. Many people remember only the headlines; here are a few of them:


Low-carb diets improve cholesterol long term (Medicinenet)
Low-carbohydrate diet beats low-fat diet in decreasing heart risk (Thaindian news)
Low-carb diet better for heart health than low-fat diet (The Money Times)


Low-carb, low-fat diets tied for long term weight loss ( (University of Arkansas for Medical Sciences)
Study disputes low-carb diet concerns (Philadelphia Inquirer)
Low-carb diet as good as low-fat one (Press TV)

When people do studies of "low-carb" diets that include 150 grams of carbs, low-carb supporters scream that such diets aren't really low carb (and I agree with this), that if they'd tested 50 g or 30 g or 20 g a day, they would have seen different results.

In this case, the low-fat supporters are screaming that a diet with <30% fat isn't really a low-fat diet, that if they'd limited fat to 10%, they would have seen different results.

I agree that this study would have been better if they'd tested 4 different diets: very low carb ketogenic diet (<50 g carbs), low-carb diet (50-130 g), low-fat diet (<30% fat), very low fat (<10%).

But I think the researchers were trying to compare a standard Atkins diet (the diet many people think about when they think low carb, even though there are other low-carb diets that I think are better) with "standard care," which still often means following the old Food Pyramid with 60% carbs and <30% fat.

They may also have worried that few of the study subjects would have been willing to stick to the stricter diets for 2 years or more. Even with the more moderate diets, attrition was high: 32% for the low-fat diet and 42% for the low-carb diet at the end of 2 years.

The low-fat diet was limited in calories; the low-carb diet was not.

Both groups lost weight, rapidly at first, reaching a nadir at 6 months, and then regained some of the weight, so that by the end of 2 years, they'd lost an average of 7% of their starting weight.

Interestingly, this was the goal in the Diabetes Prevention Program weight-loss study of people at high risk of developing diabetes. The DPP showed that modest weight loss (the goal of 7% was not actually reached) could reduce the risk of progressing to overt diabetes. The same phenomenon occurred in that study too: subjects initially lost weight fast, then leveled off and started regaining again.

I think we've all experienced this phenomenon. We try a new diet and are enthusiastic and follow it exactly. Then after some time we hit a plateau and we also get bored with the diet and gradually revert to our old habits.

It's also possible that the body wants to maintain a certain weight that is higher than the weight we want it to have (the set-point theory), and after some time the metabolism changes to encourage the regaining of the weight.

People will never agree on the best diet for weight loss, partly because different people do better on different diets: YMMV, or "Your mileage may vary." But the more we know about various diets and various groups of dieters, preferable for as long as possible, the better.

Like weight loss, lipid levels tend to be different in the short term than they are in the long term. For example, in this study, triglycerides rapidly decreased in the low-carb group but then went up again and by the end of 2 years were about the same as the levels in the low-fat group. LDL levels went up in the low-carb group but later went down again. Only HDL levels were consistently higher on the low-carb diet throughout the study.

It's not clear whether the fluctuating lipid levels were because after 12 weeks the people on the low-carb diet were instructed to slowly start adding back carbs until their weight stabilized. This is what Atkins told people to do. But in fact, the weights in the low-carb group continued to drop after 12 weeks and then instead of "stabilizing" started to climb.

So it's also possible that the body was adapting to a different diet and adjusting the lipid levels after a certain amount of time on the diet. Perhaps we have a "lipid set-point" as well as a weight set-point, and the body keeps trying to reach it.

Regardless of the reasons for these shifts, in order to really understand how diets affect various heart health risks, we need longer-term data. Foster and colleagues have made a valuable first step. Perhaps even longer studies will follow.