David H. Freedman

To hear (for example) the Los Angeles Times tell it, there has been a reversal of opinion about what causes people to be overweight and unhealthy. Specifically, it used to be all about fat, but now experts realize it’s all about carbs.

Really? I don’t think that’s even close to being a fair representation of the consensus of expert opinion over the years or now. It’s true, eating very-low-fat was all the rage in the 90s, and there has certainly been a lot of noise made more recently by people who claim eating very-low-carb will solve our weight and health problems. But the fact of the matter is that a pretty large percentage of experts–or at least those experts who have actually been directly studying and working with significant numbers of overweight people and helping them lose weight–have fairly consistently maintained that the real problem is taking in too many calories and not burning enough of them. Yes, reducing fat was considered the prime target for many years, and reducing refined carbs is considered an especially good target right now, but for most experts the real goal is and has been all along to reduce intake of calories, and reducing both fats (especially saturated fats) and carbs (mostly refined carbs) has been and continues to be seen as an especially good way to do that. I’m 56 years old, and when I was a kid everyone knew that eating foods loaded with sugar and flour was a terrible idea if you were trying to lose weight–and it wasn’t exactly breaking news then, either. It’s just plain silly to claim that there has been a recent realization that excess consumption of sugar and white flour is a big contributor to obesity.

So why do some journalists seem convinced there has been a massive shift in opinion? Part of the problem, apparently, is that although obesity tremendously increases heart-disease risk, heart disease is actually one of the few serious illnesses that modern medicine has been able to get at least a bit of a handle on, and the mortality numbers for heart disease have been improving. But that good news has been somewhat offset by the fact that Type 2 diabetes is becoming a much bigger problem in society, and while that disease is also closely linked to obesity, excess consumption of refined carbs does indeed seem to be an especially risk-raising factor. That’s what the LA Times article emphasizes.

But what that article and many others overlook is that while certain types of foods may play special roles in raising risks for particular diseases, obesity tends to be the overriding risk factor. Staying at a healthy weight, almost regardless of how you do it, is what’s most likely to lower your risks of heart disease, diabetes and cancer (not to mention other benefits such as increased energy and mobility). If you eat very-low-carbs but end up overweight anyway you’ll be at much higher risk of disease than someone who manages to get to and remain at a healthy weight while continuing to eat generous amounts of carbs. Relatively few experts dispute this fact.

What’s really at issue, then, is whether being on a very-low-carb diet is more likely to help you lose weight and keep it off permanently than are other types of diets. You’ll hear very-low-carb advocates (like the experts quoted in the LA Times article) citing all sorts of studies in which these diets brought on impressive weight loss, with of course the expected improvement in health markers that almost always goes along with losing weight. But please, before you ever allow yourself to make any weight-related diet or other lifestyle decisions based on any of these studies, do yourself a huge favor and do the following two things. First, note how long the study went on for, and if it’s less than two years, ignore it completely. Researchers have been able to get people to lose weight on just about any sort of diet or lifestyle modification–a point colorfully illustrated recently by the professor who lost weight on a snack-cake diet. But researchers are usually not able to demonstrate that special diets enable people to keep the lost weight off for much more than a year, and often these studies (like the one most prominently cited in the LA Times article) only last a small number of weeks. Second, if you come across a long-term study that seems to suggest a particular type of diet did the trick in helping people keep the weight off, make a point of looking up other diet studies to see for yourself that advocates of other types of diets can make the same exact claims. The bottom line: studies in aggregate don’t clearly support any particular type of diet over others for long-term weight loss. If you’ve been reading other posts in this blog, you know what I’m going to say now: The way to lose weight and keep it off is to make gradual, comfortable, modest changes in your diet and activity so that you slowly move towards eating healthier, less-calorie-dense foods and more daily physical activity as routine, lifelong habits.

Now having said all that, let me say, as I’ve said all along, that (preferably gradually) reducing your intake of sugars and other simple carbs (especially by subbing in other, preferably less calorie-dense foods) is a great goal in a behavior-change-oriented approach to losing weight. Simple carbs often make up a huge percentage of calories in many people’s diets. Yet they are among the biggest offenders when it comes to providing that insidiously wonderful sensory experience that serves as toxic instant gratification for people who tend to overeat. What’s more, simple carbs are metabolic gunpowder, in that they tend to spurt as sugar right into the bloodstream, which (to oversimplify a complex picture) causes the body to overreact by producing too much insulin and quickly removing all that sugar. In other words, simple carbs cause your blood sugar to spike and then plunge. The result of a plunge in blood sugar is that you feel hungry. So eating simple carbs not only rewards you for overeating on a sensory level, it also makes you hungrier. Or at least that’s how it seems to work for many and probably most people. (And a constantly repeated carb-exacerbated blood-sugar spike and plunge can also eventually help bring on Type 2 diabetes, which is why simple carbs are linked to the disease.)

So yes, people who want to lose weight should generally make reducing simple carbs a key goal. But–and this is a big “but”–there is very little evidence that going quite a bit further and virtually eliminating your intake of carbs altogether, including complex carbs such as whole-grain foods and beans and other legumes, is a very good idea at all. And yet doing so is exactly what a very vocal group of ultra-low-carb extremists insists we all must do to become healthy. The ultra-low-carb crowd doesn’t merely claim that its approach is a good way to lose weight. It doesn’t even merely claim that it’s the best way to lose weight. It claims that it’s the only way to lose weight. That’s right–according to these folks, it’s not biologically possible to lose weight and keep it off unless you drastically cut down on your intake of all carbs, because carbs make your body produce fat, whereas other foods go into fueling muscle activity. They “prove” that this is true by detailing metabolic processes at great length and citing all sorts of studies, relying heavily on rodent studies and short-term weight-loss studies. And of course they highlight their own personal successes with very-low-carb diets. (By the way, when I say “all” carbs, I’m being a little imprecise. In fact, even ultra-low-carb enthusiasts recognize that fiber of the sort found for example in green vegetables, though it’s technically a carb, is fine and even desirable in your diet. So understand when I say “carb” I’m leaving fiber out of it, because there’s just no controversy there.)

Please don’t mix up the good advice to significantly reduce simple carbs with the somewhat extremist advice to almost entirely eliminate all carbs. The former is considered good nutritional advice by just about everyone, and in fact it really more or less always has been. The latter, which is of course essentially the Atkins diet, is considered to be not a good idea by most experts–the Atkins diet is widely considered a fad diet. Why? Well, for one thing, as appealing as it may be to imagine that all you need to know about weight loss is that fat just melts off when you cut out carbs and comes flying on when you don’t, the ultra-low-carb crowd has to do some pretty amusing backflips to explain how whole swaths of the planet (especially in Asia), and countless thousands of people in studies, and probably many people you know personally (maybe you yourself!), have managed to stay trim, and in many cases lose weight and keep it off, while still eating at least moderate amounts and in many cases plenty of all kinds of carbs. Needless to say, low-fat proponents present a different picture of how the metabolism deals with different types of food and cite different studies to produce an equally impressive-sounding (and possibly ultimately equally specious) case that reducing fats is the secret to losing weight. What’s more, many and possibly most experts are concerned about the possible negative health effects of diets that are extremely low in all carbs, at least in part because these diets are inevitably very high in fats. (Most ultra-low-carb extremists insist eating loads of saturated fats is perfectly healthy, and that especially worries a lot of experts.)

But to me, while these objections are well worth considering, they’re not the biggest problem with the claim that we all need to cut out all our carbs. The biggest problem would be that the ultra-low-carb diet, having received all kinds of publicity over the past 40 years, has by now been tried by tens of millions of people, and by all evidence only some minute fraction–perhaps a few percent–actually end up staying with it and keep on not eating carbs for many years. Is that surprising to you? Do you really think you can give up not only all sugar and white flour, but all grains, beans, fruit, rice, and potatoes for the rest of your life? Come on–this is a massive, drastic change in behavior, and it has to take place and permanently stick in a world where these delicious foods are ubiquitous and highly appreciated, and have always made for a significant part of just about everyone’s diet. Short of making carbs disappear from the planet overnight, I just think it’s silly to imagine some significant percentage of the population swearing them off and being able to hew to that plan for the rest of their lives. That’s why when you talk to people about the Atkins diet you hear the same story again and again: Tried it, lost weight without being terribly hungry, thought it was the greatest diet ever, eventually got cravings, cheated a little, cheated even more, caved in and went back to carbs, gained all the weight back and more. Yes, there are apparently thousands of people out there who really seem to have adapted to a permanently carb-free lifestyle. I say congratulations, and more power to them. But remember, take any goofy idea and you’ll find thousands of people out there who have made it work for them, and who then become determined to convince the rest of the world that it’s the only way to go. Some articles in the mass media, like the LA Times article, vaguely make it sound as if the experts widely back this extreme point of view. But go and search out other articles that back this point of view, and you’ll see the same handful of experts trotted out to make the same claims. They’re a real minority among experts in the field.

When you read about some study that shows reducing carbs helps with weight loss and health, or about some expert stating what a good idea it is to lower carbs, don’t assume they’re talking about the extremist position of near-total carb elimination. Journalists may occasionally conflate the two very different positions to suggest there has been some giant sea-change in thinking about carbs, but it’s not really the case. Yes, it’s fair to say there is now more attention being paid to carbs than before, and reasonably so, but the basic advice has actually been fairly consistent for decades: Take it easy on simple carbs and especially sugar, and take it easy on fats and especially saturated fats, because these are both sensory-stimulating, high-calorie-density foods. These are well-established strategies that have been known for decades to help with weight loss that can be permanently maintained.

Now quit reading blogs and go out and take a brisk walk. Then come back and reward yourself with a small bowl of your favorite complex carb.