Discuss Raw: Weight gain on a carbohydrate based diet

There's a claim going around that you can't gain weight (fat)on a high carbohydrate, low fat diet. As far as I can tell, this belief is based on the work of Colin Campbell, Neal Barnard and/or personal experiences.

Whilst observing the diets of Americans and rural Chinese, Colin Campbell noticed Chinese people ate more calories than Americans but were slimmer. He put this partly down to them being more active, but also felt that their low protein diet may have played a part, as rodents, and pigs, fed low protein diet gained less than those fed high protein diets.

I've only seen one study done on humans showing similar effects. They were given high and low protein diets. Overall, people gained less weight on the low protein diet, but for some people the effects of the two diets weren't significantly different. Some even did better on the high protein diet.[1]

Some say thermogenisis mops up any excess carbohydrate calories. A few studies have found that thermogenisis is higher on high protein diets.[2][3] This makes sense as you'll see.

What is thermogenisis or the thermic effect of food?

The thermic effect of food is nothing more than the energy used digesting food. The harder a food is to digest, the higher the thermic effect and the more energy you burn. Out of the three marco nutrients, protein has the highest thermic effect. The thermic effect of protein is 10 – 20% of calories. The thermic effect of carbohydrate is 5 – 10%, and the thermic effect of fat 0 – 5%.[4] This means fat is the easiest macro nutrient to digest. Not carbohydrate as many people believe.

This means a high carbohydrate diet will have a higher thermic effect than a high fat diet with the same protein level. However, a lot of high fat diets are higher in protein than many low fat diets. This might make the difference in thermogenisis less significant.

In a study comparing the thermic effect of different types of carbohydrates, sucrose had the highest thermic effect. 10 healthy males were given 75g, or 300 calories, of each carbohydrate. Over a six hour period, they lost 33 calories, due to thermogenisis, with sucrose.[5] This is nothing to get too excited about.

If you think higher fibre sugar sources will lead to higher levels of thermogenisis, you're wrong. Lower fibre meals induce thermogenisis more than higher fibre meals.[6] There are other nutrients in whole foods that might increase thermogenisis slightly, but lets not over think this. Thermogenisis is merely the energy used to digest food.

What about fat storage?

As with digesting, energy is needed to store energy as fat. Storing fat as fat doesn't require much energy. However, carbohydrate uses 23% of the energy.[7] With this in mind, you should gain less weight over consuming on carbohydrate than fat. Instead of storing 975 out of 1000 excess calories, you would store 770. This is still weight gain.

Assuming you didn't exercise more to burn it off, if you consumed an excess of 500 carbohydrate calories a day for 1 month, you would theoretically gain over 1kg of fat.

500 – 50 (max energy used digesting) = 450 – 104 (energy used converting to fat) = 346 divided by 9 (calories in a gram of fat) = 38.4 (grams of fat) x 28 (4 weeks) = 1076g = 1.08kg

A study done on overfeeding fat and carbohydrate supports this. Fat overfeeding led to 90 – 95% of the excess energy being stored. Carbohydrate overfeeding led to 75 – 85% of the excess energy being stored.[8] Another slightly longer study, found no significant differences between overfeeding on fat and carbohydrate.[9]

Unlimited calories and weight loss

Some people may be aware of Neal Barnard's study where they put people on a low fat vegan diet, and were told they could eat as many calories as they wanted. They lost weight and their diabetes improved. Does this mean you can eat unlimited calories and not gain weight, or lose weight even? No. They were allowed to eat as much as they wanted, but they averaged at about 1400 calories a day, down from an average of 1800 calories a day.[10]

Discuss Raw

Tuesday 4 December 2012

Weight gain on a carbohydrate based diet

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