Low Carb Diets: How Come They Don't Make Us Fat?

Low carb diets work, at least according to lots of evidence and clinical data accumulated over the past century. The debate about how they work -- or whether they work better than low calorie diets -- rages. But very few people take the time to acknowledge how weird it is that a high fat diet could possibly lead to weight loss at all.

After all, if "a calorie is a calorie," and if fats have more than twice as many calories per gram than do carbohydrates, shouldn't people who eat lots of butter, steak and bacon be fatter than people who restrain themselves and eat melba toast and oatmeal?

The obesity research community loves to tout the talking point that 'a calorie is a calorie' as if it were carved in stone. To the conventional nutritionist, what counts is the number of calories we ingest and the number of calories we burn via activity. We're reminded to 'watch what we eat.' We're told to take the stairs instead of the elevator. We're advised to spend time outdoors and to stay away from the computer and the TV.

The alternative theory, the Lipophilia Hypothesis, says that carb restriction and other measures to control insulin should lead to weight loss -- even if a person eats a diet that's unrestricted in calories and doesn't increase his or her level of physical activity. According to this theory, insulin controls fat accumulation. Control insulin, you control fat. Calories are beside the point.

For Caloric Balance to make any sense of why carb restriction might lead to weight loss, these diets must ultimately be "calorie restriction by another name." Indeed, many advocates of carb restriction have bought into this idea. Even John Yudkin -- whom Gary Taubes describes as a key pioneer of the low carb diet science -- insisted that 'low carbohydrate diets were low calorie diets in disguise' and talked about 'the inevitability of calories.'[1a]

But an avalanche of evidence shows that low carbohydrate diets can work even when they're unrestricted in calories:

1. For more about these studies and the theories behind them, please see Chapter 20 of Good Calories Bad Calories (pages 327-354).[1b] In many studies referenced, subjects lost weight without hunger and lost weight even on calorie intakes that far exceeded those recommended by traditional low calorie diets.

2. Evidence from anthropology also abounds. The indigenous Inuit and Maasai warriors stayed lean despite eating copious amounts of fat and eating calorie-unlimited diets, for instance.

3. For anecdotal success stories about calorie-unrestricted low carb diets, just do a cursory check on the internet. Review posts from people who've tried these diets:

The theme you'll encounter again and again is: if you control insulin by controlling carbs, you can lose weight. Calories don't seem to matter!

4. Low carb diet studies confirm this phenomenon. Consider this randomly selected article -- an article that appears biased against the low carb approach!:

"Three well controlled studies now show that after following a low carb diet for six months, people generally have lost more weight than those on more traditional low fat diets. In fact, average weight loss of those on low carb diets is two to three times as much after six months. These diets also offer the advantages of producing greater drops in blood triglyceride levels. They improved blood sugar and insulin function in people who originally showed abnormalities. The increased blood cholesterol that experts expected generally did not show up. Fewer people dropped out of the low carb diet groups at six months, too, maybe partly because of the encouragement they received from rapid early results."[2]

Proponents of calorie restricted diets can look at clinical studies like these and try to poke holes in them. That's good. Science works by a process of relentless skepticism.

But pro-low-carb-diet evidence continues to stack up. And it's nearly impossible to identify compelling evidence to support the low calorie diet.

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1a. Taubes, Gary. "Good Calories, Bad Calories." pp 410-411. New York: Knopf (2007).

1b. ibid pp 327-354.

2. Collins, Karen. Defining the success of low-carb diets MSNBC (Aug 20, 2004).

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