The good news: Despite how challenging, annoying and frustrating (hey, we’ve all been there) a weight-loss diet can seem at the beginning, if you stick with it, you’re likely to feel happier within a few weeks.

The bad news: If you’ve chosen a low-carb weight-loss plan (like the Atkins diet), that improved mood may fade away. After a year, you’re likely to feel the same as before you began to shed pounds.

Your mood won’t be any worse, but it won’t be any better, either.

That’s the central finding from an Australian study published this week in the Archives of Internal Medicine. The researchers enlisted 106 overweight and obese volunteers, who were randomized to either a low-carb, high-fat diet (like Atkins) or a high-carb, low-fat diet (like the “Mediterranean” diet).

At the end of a year, both groups had lost about the same amount of weight (on average, about 30 pounds each), and both also scored about the same on tests that measured their short-term memory and speed-of-processing thinking skills. (The memory skills, by the way, improved for both groups.)

But, the people on the low-fat diet were more likely to enjoy a sustained boost in mood. Specifically, at the end of the year they scored better on tests that measured anger-hostility, confusion-bewilderment and depression-dejection.

Harder to follow?
Why would a low-fat diet be better at enhancing mood over the long run?

The researchers aren’t sure, but they speculate that it might be tougher to adopt a low-carb diet in our Western culture, which tends to favor carbohydrates like bread, pasta, rice and fruit. Or low-carb diets may just be harder for individuals to follow. Both factors could dampen a low-carb adherent's mood.

Or, it may be that low-carb diets produce less serotonin, the brain chemical associated with feelings of happiness and well-being.

It’s important to note, however, that the mood states of both groups fell well within the normal range for healthy adults throughout the study. So we’re not talking about any major emotional problems here.

Nor is this study the final word on this topic.

Still, it would be nice to feel somewhat happier after losing 30 pounds, wouldn’t it?