In a recent post, I speculated on reasons why people are obese. In many ways, this current post is the opposite: why do low carb diets reduce obese people to slender people? There are a lot of claims on the Internet about why low carb diets work, some of them quite outrageous, and I want to seek wisdom on this topic.
The Carbohydrate Hypothesis. Gary Taubes is the leading proponent of the hypothesis that carbs, especially refined carbs like flour and sugar, are fattening. This is also known as the "carbohydrate hypothesis." According to Taubes, carbs lead to insulin spikes, which leads to fat deposition (accumulation). The "carbohydrate hypothesis" is widely disputed and to date, there is no empirical evidence to back it up, though Taubes is apparently trying to raise money for such an empirical test. Personally, I no longer believe this theory, though at one time, I was a believer. True believers in this hypothesis include Jimmy Moore, Dana Carpender, Gary Taubes (of course), and Tom Naughton, among many others.
Metabolic Advantage. Others suggest that a low carb diet gives you a metabolic advantage (the idea that you burn calories more efficiently while low carbing, and can therefore consume greater quantities of low carb food and still lose weight), though at present there is very little empirical evidence to back up this claim. This idea is also widely disputed, as exemplified by the dust-up between Michael Eades and Anthony Colpo on this very topic. The metabolic advantage theory leads to the idea that calories don't count, that some calories (e.g., "low carb" calories") are better than other calories. Thus, if you eat low carb, you don't have to worry about calories. I am also on record as rejecting this idea.
Satiety. Another theory about why low carb diets work is that protein and fat are more satiating (see this article, too). When you eat a high fat, moderate protein, low carb diet you lose weight because you spontaneously consume fewer calories. There seems to be a lot more evidence for this theory (e.g., here, here, and here). Note, too, that this theory implicitly rejects the theory of metabolic advantage mentioned above. I am on record as saying this is a major reason why low carb works.
Toxins, Infections, and Malnutrition. The Perfect Health Diet maintains that weight loss happens when you eliminate toxins from your diet, as well as malnutrition and infections caused by your diet. The Jaminets have developed a diet based on these three ideas, which is summarized here. The diet is a low carb diet that includes so-called "safe starches," such as potatoes and white rice. A "safe starch" has nothing to do with carb or glucose content. It is a term invented by the Jaminets and "refers to any starchy food which, after normal cooking, lacks toxins, chiefly protein toxins. We do not consider glucose to be a toxin, though it may become toxic in hyperglycemia" (reference). Their definition of a low carb diet is one between 100 to 150 grams of carbs per day, mostly from "safe starches," as a low carb diet for them "means eating less than the body's actual glucose utilization, so that a glucose deficit has to be made up by gluconeogenesis" (reference). But weight loss happens not because carbs are reduced, but because toxins are eliminated, infections are reduced, and malnutrition is aggressively attacked. I am currently following the Perfect Health Diet, so I guess you could say I am a believer in this hypothesis.
Low Carb Works by Accident. Kurt Harris, M.D., maintains that low carb diets work by accident. Specifically, he says:
Low carb plans have helped people lose fat by reducing food reward from white flour and excess sugar and maybe linoleic acid. This is by accident as it happens that most of the "carbs" in our diet are coming in the form of manufactured and processed items that are simply not real food. Low carb does not work for most people via blood sugar or insulin "locking away" fat. Insulin is necessary to store fat, but is not the main hormone regulating fat storage. That would be leptin. (emphasis added).
Food reward is an idea championed by Stephan Guyenet and the basic idea is that highly palatable foods lead to obesity. Lowering food reward, or palatability, by reducing refined sugars, flours, and even salt and other spices to produce more bland eating options leads to losing weight. The idea proposed by Harris and Guyenet is that low carb diets work, not by design, but by accident. By following Atkins, for example, you naturally reduce food reward by eliminating a whole macronutrient category, carbohydrates. As the Harris quote above indicates, he (and Guyenet) both reject Taubes' carbohydrate hypothesis.
This is a curious argument, one that makes a certain amount of sense. Why does Atkins work? If you follow Atkins, you eliminate two major problematic foods: refined sugars and refined flour. This will naturally lead to weight loss. Atkins is not too concerned about seed oils, though, which is why I don't claim to be following Atkins. My version of a low carb diet has eliminated seed oils from a very early stage in my weight loss history. Atkins also produces a lot of junk food, made with wheat gluten, soy, and other products I don't consume. An Atkins low carb diet is not necessarily a low calorie diet, if you eat too much low carb junk food. So I do think there is an element of "accident" in why low carb works.
My Position. I believe low carb works because 1) protein and fat are more satiating than carbs; 2) low carb eating causes me to spontaneously consume fewer calories, since protein and fat are more satiating than carbs; 3) calories count, so be mindful of how much you eat; 4) low carb lowers food reward by eliminating sugar, flour, and seed oils, especially those three in combination; 5) low carb removes toxins, reduces infections, and corrects malnutrition; 6) low carb requires that I eat real foods, the kind that are not processed; and 7) low carb simply offers fewer food choices. It is a lot harder to snack and harder to eat out, at least in the U.S.A. This means I eat real food cooked at home more often than not. Fortunately, my desire to snack is greatly reduced thanks to the satiety of what I eat.
I do not believe in the carbohydrate hypothesis and reject the notion that carbs are inherently fattening (this idea seems to be widely believed and held on the Internet). Rejecting this idea opened my mind to the idea of eating "safe starches," as defined by the Jaminets. I also reject the idea of metabolic advantage and believe that calories count. Thus, I would never substitute a cup of heavy cream for a cup of whole milk, simply because there are fewer carbs in the cream than in the milk, nor would I add 12 tablespoons of fat to two pounds of meat to increase the fat content of my diet That is simply too many calories and a low carb diet is already a high fat, moderate protein, low carb way of eating. You don't need to add a lot of additional fat.
Taken together, the seven reasons cited above are a recipe for low carb success.