Excess Carbohydrate Does Not Turn To Body Fat


Rice and beans, a staple food of many cultures around the world.

Dr. McDougall, in his March 2009 newsletter, discusses “de novo lipogenesis,” a term that describes the pathway for converting dietary carbohydrate into body fat. He says the pathway is not utilized much in humans, that “excess starch does not turn to body fat.” He provides several references to support his claim. They do indeed back the notion that excess carbohydrate or replacement of dietary fat by carbohydrate does not induce de novo lipogenesis to any substantial degree.


“A widely held belief is that the sugars in starches are readily converted into fat and then stored unattractively in the abdomen, hips, and buttock. Incorrect! And there is no disagreement about the truth among scientists or their published scientific research.5-13 After eating, the complex carbohydrates found in starches, such as rice, are digested into simple sugars in the intestine and then absorbed into the bloodstream where they are transported to trillions of cells in the body in order to provide for energy. Carbohydrates (sugars) consumed in excess of the body’s daily needs can be stored (invisibly) as glycogen in the muscles and liver. The total storage capacity for glycogen is about two pounds. Carbohydrates consumed in excess of our need and beyond our limited storage capacity are not readily stored as body fat. Instead, these excess carbohydrate calories are burned off as heat (a process known as facultative dietary thermogenesis) or used in physical movements not associated with exercise.9,13

The process of turning sugars into fats is known as de novo lipogenesis. Some animals, such as pigs and cows, can efficiently convert the low-energy, inexpensive carbohydrates found in grains and grasses into calorie-dense fats.5 This metabolic efficiency makes pigs and cows ideal “food animals.” Bees also perform de novo lipogenesis; converting honey (simple carbohydrates) into wax (fats). However, human beings are very inefficient at this process and as a result de novo lipogenesis does not occur under usual living conditions in people.5-13 When, during extreme conditions, de novo lipogenesis does occur the metabolic cost is about 30% of the calories consumed—a very wasteful process.11

Under experimental laboratory conditions overfeeding of large amounts of simple sugars to subjects will result in a little bit of de novo lipogenesis. For example, trim and obese women were overfed 50% more total calories than they usually ate in a day, along with an extra 3.5 ounces (135 grams) of refined sugar. From this overfeeding the women produced less than 4 grams (36 calories) of fat daily, which means a person would have to be overfed by this amount of extra calories and sugar every day for nearly 4 months in order to gain one extra pound of body fat.10 Obviously, even overeating substantial quantities of refined and processed carbohydrates is a relatively unimportant source of body fat. So where does all that belly fat come from? The fat you eat is the fat you wear.”

That study where women were overfed by 50% is something else. That’s like having them eat 3000 calories/day instead of 2000, in sugar no less. And they put on hardly any body fat. That reminds me of the Cubans during their Special Period, where they lost weight and lowered their rates of diabetes, heart disease, and cancer, by eating a diet of primarily rice and sugar.

Americans (and other rich populations) defeat this by eating a lot of fat. When you add fat to the mix, it’s a whole different ball game. See my posts:
“Meat And Potatoes” Dietary Pattern And Risk For Colon Cancer
High-Fat High-Sugar Dietary Pattern (“Meat & Potatoes”) Linked To Colon Cancer, Diabetes

I ran across McDougall’s discussion of de novo lipogenesis because he took issue with the following statement from that new saturated fat study I keep talking about:

“For example, the influence of metabolism seems particularly relevant for the de novo synthesis of even-numbered saturated fatty acids in the body, compositions of which are largely determined by dietary factors, including carbohydrate and alcohol consumption (33–35), and other metabolic pathways (36, 37) rather than direct dietary intake.”

If carbohydrate intake doesn’t induce de novo lipogenesis to any substantial degree, why would these authors (whose study gave saturated fat consumption the green light) say it does?

Related: New Study: Low-Protein, High-Carb Diet Offers Similar Benefits To Caloric Restriction – Without Caloric Restriction

15 thoughts on “Excess Carbohydrate Does Not Turn To Body Fat

  1. RB

    Dr. McDougall is the polar opposite of Gary Taubes (http://fanaticcook.blogspot.com/2011/04/gary-taubes-is-sugar-toxic.html). Well, do carbs make us fat or does fat make us fat?

    From you post https://fanaticcook.com/2014/03/23/that-saturated-fat-study-harvard-responds/ It think Dr. McDougal thinks: “When people think “carbohydrates,” do they think … carrots and apples? Do they think beans and lentils?” And Gary Taubes thinks: “Or do they think highly processed, white-flour-white-sugar breads, boxed breakfast cereals, bagels, pretzels, crackers, cookies, cakes, muffins? “


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  3. sally

    So does that mean as long as you keep the fat intake as low as possiblel for eg 2-3% that you could even eat like 20 Sounds of potatoes without gaining weight??! Sounds kind of unrealistic to me
    Btw great blog


    1. Bix Post author

      Hi Sally,

      When Chris Voigt ate only potatoes, 20 a day for 60 days, he lost weight and body fat. His blood sugar went down too. In the 1990s, the Cubans lost weight and reduced their incidence of diabetes, heart disease, and cancer when they lowered their fat intake (to ~15%) while eating a diet of primarily rice and sugar.

      Since these things really did happen I would call them realistic.


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  5. Pingback: What Is The Fate Of Excess Carbohydrate? Does It Become Body Fat? | Fanatic Cook

  6. Tina

    But the new celebration of “healthy fats” and ketogenic diets is a very recent pheomenon. If that’s true, why did so many people constantly gain weight since the 80ies while eating all of those terrible industrial zero fat products? I really want to believe this, because I really like starches – but I DID gain weight in the past while on a pinapple and also while on a rice diet.

    From my own experience, what keeps weight under control is phases of water fasting. Ideally I would like to alternate between eating a vegan high starch diet at the other days, but it is just so, so much easier to transition into fasting periods coming from a high fat diet. When I eat starches, I constantly oscillate between feeling too full and feeling hungry again – phases of happy equilibrium in between are very short, whereas on high fat feel the same all day. I know this is “anectdotal”, but does that mean it can be ignored. PErhaps the starch solution only works for those who are metabolically in a specific group with that glucose preference?


    1. Bix Post author

      Speaking of the rice diet, here’s the original Kempner rice diet:

      The Rice Diet: Forerunner Of Today’s High-Carb Plant-Based Diets

      Americans ate a high-fat diet from 1971 to 2000. It was always over 30% of calories from fat. They never ate a low-fat diet:

      Trends in Intake of Energy and Macronutrients — United States, 1971–2000

      Contrast that 30% with the 7% of calories from fat in the study I just posted, where people ate as much food as they wanted and still lost weight, lowered their blood pressure, blood glucose, blood cholesterol.


    2. Frankie

      I’m the same way: Ideally I could eat as many fruits/vegetables as I want, but I’ve only seen weight loss and steady energy, better sleep, etc., on vegan keto, probably due in part to the menu choices and also because I don’t retain as much water on a <20g and under net carb count.

      What I've been thinking about is how to safely transition from LCHF to HCLF without overlapping the two too closely together. The fasting idea works, but I'd also like to keep my metabolism constant and stick to a solid eating schedule. Still experimenting a bit and seeing what happens.

      I'm ~5 lbs-ish from my ideal weight, but at this point, the slightest adjustments make a big difference (and I mean if I make the wrong move, I'm up 5 lbs). Not much margin left for error, it seems.


    3. Frankie

      “Perhaps the starch solution only works for those who are metabolically in a specific group with that glucose preference?”

      I wonder about this as well. I (and my people, lol) seem to fare better on a HCLF diet, as long as those carbs come from whole foods (even processed foods don’t lead to so much weight gain unless I really stuff myself, which I was prone to doing once going vegan). However, I can never seem to be full on fats, so the weight loss pretty much begins and ends with being hungry. The body is a mysterious machine.



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