Carbohydrate Makes Us Hungry

Sugars and High-Glycemic Starches are the Worst

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In almost every weight-loss study comparing reduced-carbohydrate diets to calorie-restricted diets, the low-carb group loses at least as much weight, and usually more. It’s always been amazing to me that this is so little remarked upon by the scientists doing the work. You’d think that consciously restricting calories would produce more weight loss than a diet which basically pays little attention to the amount of food eaten.

As any experienced low-carber knows, the answer is that we are less hungry when we restrict carbs, and more hungry when we restrict calories. (Caveat: people on calorie-restricted diets have almost always cut back on carbohydrate, and this may actually account for some of the weight loss on those diets.) So why do diet researchers generally ignore this effect? Wouldn’t you think this would be a key issue to explore? But so far, it’s been pretty much….crickets.

However, recently there has actually been a little work done on this, much of it using milkshakes. Milkshakes are actually great for studying the varying effects of the amounts and types of carbohydrates, fats and proteins on metabolism. This is because they can be varied on all these dimensions, but still have the same flavor and consistency -- the participants in the experiment don’t know the difference, but the experimenters do. Let’s take a look at a couple of these studies.

1. Low-Glycemic Carbs vs High-Glycemic Carbs

This study, led by Dr. David Ludwig, gave overweight or obese men aged 18-35 two different milkshakes two weeks apart. To the men, they were the same -- they had been engineered to have exactly the same amount of carbohydrate (69 grams), protein (18 grams), fat (14 grams), and calories (500), and they tasted exactly the same.

People could not tell the difference between the milkshakes...but there was a key difference. The carbohydrate in one of the drinks was calculated to send blood sugar up higher than the other. This would be something like comparing drinking a soft drink to eating brown rice or whole cooked beans.

So what happened? Several things.

1) Blood Sugar - Of course, the high-glycemic shake sent blood sugar up higher after drinking it. But by 2 hours afterward, blood sugar from the high-GI shake was actually lower, eventually heading down into hypoglycemic territory. The blood sugar was much more stable after the low-GI shake, never dropping below normal.

2) Hunger - Every half hour for the next five hours after the shakes, the men were asked to rate their hunger. Of course, hunger ratings dropped into the "not hungry" zone on the graph immediately after drinking the shake. But even then, the high-GI shake was never as satiating. Throughout the next five hours, the men were less satiated, and then more hungry, after the high-GI shake.

That's at every single point during the five hours.

3) Brain Imaging - Much has been made of the fact that the high-GI shake triggered more activation in brain centers associated with reward and addiction. This is interesting because we know that what are called "highly palatable processed foods" trigger these centers. Heck, even pictures of those foods make our brains take notice! This study controlled for that by making the palatability of the shakes exactly the same.

But. The brain imaging was done at the four-hour mark. We already know that food reward centers are more active when people are hungry (and everyone knows that food tastes better when we are hungry). So was the difference between the shakes on the brain imaging mediated by the fact that the high-GI shakes made the men hungrier? I don't think that question has been answered. If the brain images were different soon after drinking the shakes, that would have told us more about addiction, but the imaging was not done at that point.

2. Carbohydrates vs Fats

OK, so it appears that high-glycemic carbohydrates can make people hungrier than low-glycemic ones. But people following low-carb diets usually increase the amount of fat in their diets as they cut back on sugars and starches. What happens then? You might think it would be even better, because fats don’t raise blood sugar at all, whereas all carbohydrates are essentially “sugar” to our bodies.

One study, again using shakes (4 different ones this time), looked at what happens in our brains with various levels of fats and sugar in the shakes (same calories). And guess what? The researchers were surprised to find that although all the shakes were rewarding, sugar was the component that really lit up the brain, even though all the shakes were equally sweet. A question not answered by this study: was the high-fat low-sugar shake rewarding because of the fat, or because of the sweetness, since we know a sweet taste is rewarding even without the effects on the body that sugar has.

None of this will surprise people familiar with how carbs affect their bodies. In one recent study of Mediterranean diets and heart disease, asking people to add substantial amounts of nuts or olive oil to their diets did not cause people to gain weight: they apparently just naturally cut back on some other things they were eating. Which is exactly how our bodies are supposed to work. It is only recently that people even had to think much about overweight or obesity or calories. Weight was something that peoples' bodies handled more or less automatically, using -- guess what? -- hunger. Imagine that. Could this influx of high-glycemic, highly-processed sugars and starches have upset this balance? It appears to be at least part of it.

Technical Note: I very much like studies such as these where people are compared to *themselves* instead of other random people. You can only do this in relatively smaller and short-term studies, but they tell us a lot. The same research group that did the first study I described above (Low-Carb May Be Better at Maintaining Weight Loss) also compared people to themselves when following different diets for weight-loss maintenance. It reminds us that we can do our own studies -- we don’t need to know the average results of 50,000 people; we just need to know the results in our very own bodies.

Lemmerz, Alsop, el al. Effects of dietary glycemic index on brain regions related to reward and craving in men. American Journal of Clinical Nutrition. 113.064113v1 (2013)
Stice, et al. Relative ability of fat and sugar tastes to activate reward, gustatory, and somatosensory regions. Dec;98(6):1377-84 (2013)

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