Why the sourpuss? Maybe it’s your low-carb diet

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To any dieter who has ever sworn off bread and pasta, the next sentence may come as no surprise. A new study, published in the Nov.9th issue of the Archives of Internal Medicine, shows that after dieting for one year, people following strict, low-carb diets had more bad moods than dieters eating a high-carb (albeit low-fat) diet. And, yes, the number of daily calories alloted to each group was the same, so sheer hunger was not the issue and both groups lost weight.

The foul moods were surprising, the authors note, because generally obese people who diet and lose weight feel an overall mood lift. The researchers go on to observe that, as more and more Americans struggle with their weight, very low-carb diets, which are typically high in protein and fat, are still quite popular. And that even though studies show that low-carb diets can be effective, the long-term effects on mood and cognition are not well understood.

For the study, Australian researchers recruited 106 overweight and obese adults (average age of 50) and randomly assigned half the volunteers to eat a low-carb, high-fat diet for a year. The other group was put on a low-fat, high-carb diet for the same duration.

More specifically, the total calories in the low-carb diet broke down this way: 4%  from carbs, 61% from fat, and 35% protein. In comparison, the total calories for those in the low-fat group included: 46% from carbs, 30% from fat, and 24% protein.

Periodically, scientists tested the participants for changes in weight, mood, and brain functions, such as learning and memory skills.

The good news is that one year later, the average weight loss was roughly 3o pounds in both groups regardless of diet assignment.

The bad news is that the low-carb dieters didn’t enjoy the mood boost that typically accompanies a successful weight loss. For the first 8 weeks, both groups felt an upswing in mood. But, as the year progressed, only the low-fat dieters kept the new sunny disposition. Carb-avoiders slowly returned to their pre-weight-loss levels of crankiness.

At week 52, compared to the low-fat group, the low-carb dieters scored much higher, which is worse in this case, on tests designed to measure anger-hostility, confusion-bewilderment, and depression-dejection. These results are consistent, say the authors, with other studies that link low-carb diets to greater levels of anxiety and depression. “Our outcome suggests that some aspects of the low-carb diet may have detrimental effects on mood that negated any positive effects of weight loss,” write the authors.

Although experts don’t understand exactly why low-carb dieters are so moody, they offered a couple of guesses. For starters, they point to the difficulty of sticking to the diet in a social setting when the typical Western diet is awash in pasta and bread.

They also muse that it could be the effects of eating so much protein and fat on the brain. Both may negatively impact brain levels of serotonin, a potent chemical messenger necessary for healthy brain function.

One important caveat: No dieter was on the verge of a total meltdown. Despite the significant finding between the two groups, overall mood scores for both groups remained (on average) within normal range throughout the study’s duration.

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