Is Low-Carb a Fad Diet?

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Updated from my blog post of Sept 9, 2013, commenting on an opinion piece in JAMA (the Journal of the American Medical Association) implying that low-carb diets are a "fad."

To make real headway in the obesity epidemic, it is obviously going to take a lot of people working together. One of the problems at this point is that people are working on it from a lot of different angles, and not much has been brought together in a coherent (let alone coordinated) way.

People are researching (to name only a few): our gut flora, our fat cells, our brains, our hormones, environmental toxins, exercise, and, yes, diet, all in an attempt to figure why so many people started overeating a few decades ago and what we can do about it. Each area of research has their own ideas about it, and the public health message has been garbled, to put it mildly.

In the current issue of JAMA (The Journal of the American Medical Association), two psychologists (Sherry Pagoto and Bradley Appelhans) enter the conversation with an opinion piece entitled, "A Call for an End to the Diet Debates." When something like this appears in JAMA it can carry a fair amount of influence with physicians, so it's worth paying attention to.

Their main points are that:

  • We should stop looking for an ideal diet for everyone. In particular, it doesn't make a difference vis-a-vis weight loss what "macronutrient mix" (mix of fats, proteins, and carbohydrates) a person eats, so let's stop studying it and please let's stop yacking about it.
  • "Lifestyle interventions" (which I take to mean is a vague reference to some sort of assistance with diet and exercise) are helpful. This should be more widely practiced, and insurance should help pay for it.  
  • Fad diets are part of the problem, and have "created a multibillion-dollar industry." Furthermore, "the difference between fad diets is almost entirely related to macronutrient composition (e.g. Zone, Atkins, South Beach, Dukan, Paleo)."

    First of all, we notice right away that all of "fad diets" listed are reduced-carbohydrate or low-carb diets. (The Paleo diet doesn't directly advise changing the macronutrient mix, but when people follow it they tend to reduce their carb intake at least somewhat.) Ornish, McDougall, and other advocates of very low-fat/high-carb diets are not cited as examples of fad diets. We can only guess whether this indicates a bias against carbohydrate reduction, but if the authors were trying to be fair you'd think they'd put a couple of low-fat diets in there.

    On the other hand, they say (almost in passing) that macronutrient mix can make a difference in satiety, and therefore adherence to a diet. Plus, the studies they cite which compared low-carb to low-calorie diets often used one of the "fad" low-carb diets as a template for that group. So, are they in favor of playing with the macronutrient mix or not? It seems that they probably are OK with it to an extent (as long as you don't purchase a diet book?), carefully noting that a lot of things affect adherence to a diet, including food preferences and traditions. I'm curious whether the authors, both of whom have expertise with weight loss, have a method for helping people zero in on the best macronutrient mix for that person.

    And just how strongly should we weight food preferences (candy? doughnuts?) in helping a person to make dietary changes?

    Points of Agreement

    There are several areas in which I'm in total agreement with Pagoto and Appelhans, though I may have a different slant on those issues.

    1. It would be wonderful if we could abandon the search for a one-size-fits-all diet. If there's one thing that those comparison studies have shown us, it's that there is often a huge variation within each group in response to different diets (even though the averages often are similar, at least in terms of weight loss). Instead of continuing large randomized trials, I would like to see more work done identifying who responds to which interventions.

    1. Certainly, people need more support for changing diet and exercise patterns. I even would argue that people who respond to carbohydrate reduction may need special attention, simply because care providers are much more likely to have experience supporting people with low-calorie diets. This is especially heartbreaking to me personally when diabetics have difficulties finding dietitians and other providers who support a low-carb approach. I have probably received hundreds of emails by now from people who find that a low-carb diet controls their blood glucose best, but feel they are left entirely on their own to manage it (this is despite the fact that the American Diabetes Association supports a low-carb approach as an option.) 

    Points of Clarification

    1. Pagoto and Appelhans say that "additional trials comparing diets varying in macronutrient content most likely will not produce findings that would significantly advance the science of obesity". While I agree that continuing to do the same studies over again (which often seems to be the case at this point) would not be helpful, there are a glaring problems with many of those studies (Two examples: 1) the definition of "low-carbohydrate" in these studies is highly variable, so we don't even know whether we are all talking about the same thing, and 2) compliance issues: New flash: people often don't eat what they are told to eat. We need to be measuring the effects of what was actually eaten, instead of what the participants were told to eat. If these problems were addressed, the studies potentially could give us more information than they have been doing. Also, there is a great deal of more targeted work taking place -- smaller studies looking at the effects of different macronutrient mixes on various metabolic processes, hormonal pathways, etc. This type of research definitely "advances the science of obesity" (which is not at all the same thing as "the science of weight loss," BTW.)
    2. While it's true that different mixes of proteins, carbs, and fats may be more satiating for different people (therefore making it easier to stick to the diet), there is a related but independent factor, and that is the effect of a diet on cravings -- the sometimes constant intrusive thoughts about food that plague many people. Certainly one of the things that people who respond to low-carb diets love the most is the elimination of these impulses to eat. This may sometimes be confused with satiety, but I would argue that they are actually totally different experiences.
    3. About adherence to a diet: What a person may be able to stick to in the short-term may be very different from what is tolerable to carry out for years. Careful experimentation is needed each step of the way. For example, a person on a low-calorie diet often has increasing levels of hunger as the months and years go by, while a person on a low-carb diet may just get tired of eating differently from their families. People need support in navigating options when they run into obstacles.

    Points of Disagreement

    1. It isn't all about weight loss, and focusing exclusively on weight loss downplays the effect that different macronutrient mixes can have on other aspects of health. Sure, two diets with the same number of calories are going to produce approximately the same amount of weight loss (although I will note yet again that people on low-carb diets tend to lower their calorie intake spontaneously, which should provoke more awe and wonder than it seems to). Low-carb diets have been shown over and over to improve the components of metabolic syndrome in people who have that condition, and this can be true even without weight loss -- in fact, it's been estimated that up to 20% of people with BMIs in the normal range have metabolic syndrome, and they also can respond favorably to carbohydrate reduction. For some diabetics, a low-carb diet enables them to control their blood glucose without medications, or at least reduced medication, even when they are not losing weight. Are we truly going to tell them that it doesn't matter what macronutrient mix their diet is?
    2. Of course, I'm going to disagree with any implication that a low-carb diet is a fad diet. The idea that everyone does great with lots of glucose is simply wrong. In fact, as a population, our glucose tolerance seems to be decreasing over time.

    I think conversation among the different disciplines is vital while we figure out the best way to deal with this relatively new problem, and I welcome the contribution of behavioral scientists. Unfortunately, I don't see a lot of engagement between experts from various fields. Perhaps JAMA could play a role in stimulating this sort of cross-fertilization.

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