Carbs (Alone) Won’t Make You Fat

Click the image below to read Berkeley professor Marc Hellerstein explain that the body makes very little fat from de novo lipogenesis (DNL) of dietary carbohydrate, so carbs by themselves won’t make you fat. However, eating carbs with fat results in a “fat sparing” effect (consumed carbs are burned instead of fat), causing dietary fat to make a beeline for storage in our adipose tissue.
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This pretty much explains both why low-fat (< 10%) diets work, and why low-carb’ers avoid all carbs in their high-fat diets. Both are right, kind of. The low-fat crowd knows that excess dietary fat goes right into storage. That’s right, of course. And low-carb’ers think that carbs cause insulin spikes which makes your adipose tissue store serum glucose as fat (the alternative hypothesis of obesity, aka “carbs make you fat”). But, that’s extremely overstating the effect of DNL, which is tiny (normal diets in healthy people won’t generate but a few grams of fat a day), while ignoring that fat gets stored directly as fat (the “fat sparing” effect). So carbs make the body store dietary fat as fat, not glucose as fat. Someone please tell Gary Taubes that it’s

food -> insulin -> serum triglycerides -> adipose
and not
carbs -> insulin -> glucose -> adipose

They measured DNL with doubly labeled water and other accurate means. And they’ve traced dietary fat accumulation a long time ago. This is well-known stuff by now. And yes, no-carb meals will also raise insulin levels (and glucose levels).

So, if you eat little fat, you won’t have any serum triglycerides to store as fat. It’s pretty easy to eat less than 50g of fat a day when you’re motivated to lose weight. Plus, all my biking burns way more than that. Yes, fat would make meals more “satisfying”, but it would also slow down progress to my weight goal. I can live without eating it for a while. I’m not starving. I’m eating more than 600g of carbs a day.

But people will believe what they want, and they’ll blame carbs for making them fat, mostly because they like fatty foods. Personally, I’ll go high-carb, low-fat when I want to lose weight, then go to reasonable fat (30%) for maintenance.

So I ate a huge loaf of sourdough yesterday (~ 600g), and ate a bunch of noodles and tortillas today. I ate very little fat yesterday (only some Thousand Island dressing on a salad). And of course, I rode about 240 km this weekend. Today alone, I burned 2600 calories on a 4.5 hour Moment Cycles shop ride.

I don’t mind burning off a bunch of fat while I bonk at the end of a long ride. I just don’t want to eat a bunch of fat afterwards to replace it. I collapsed at Dos Brasas at the end of the ride, and drank 3 large Diet Cokes and ate an order of 3 plain tortillas to make the last 5km home. (I only ate about 1200 calories on the ride — 1.5 bagels, a regular Coke, two packs of Shot Bloks.)