How do low-carb diets affect mood?

The promise of many popular diets often includes not just weight loss, but a happier outlook. Yet, a new study shows that the expected mood improvement—the added perk usually seen when losing weight—seems to be short-lived in successful dieters on a low-carb diet.

The low-carb diet debate is one that doesn’t seem to want to fade away. The diet itself is an old one. The idea that eliminating most carbs as a weight-loss strategy is an idea that preceded Dr. Atkins by more than a century. There are many types of low-carb diets with varying restrictions on the types and amounts of carbohydrates permitted. Just like other diets, they work as long as you eat fewer calories.

Their relative popularity is at least partially because proponents find low-carb diets easier to follow: It may be that a low-carb diet produces more satiety and reduces appetite, and the initial weight loss might be greater than with other diets (although some of that initial weight loss advantage is probably explained by greater water loss).

Whether a low-carb diet is a sustainable plan is a whole different issue.

In order to lose weight on low-carb diet one needs to reduce total calories and do so over the long-term. Unfortunately, low-carb diets generally aren’t easier to stick to over the long run and the long-term weight outcomes of low-carb diets are no different than those of other diets. In fact, a large study published in the New England Journal of Medicine compared low-carb and low-fat diets and found that after a year, people dropped out of both diets at similar rates.

Many experts also worry that a low-carb diet, which replaces carbohydrates with foods containing a higher percentage of proteins and fats and especially saturated-fats, isn’t a healthy way to eat over a long period of time. Studies of low-carb diets continue to examine their effect on a multitude of end results, from heart health, atherosclerosis and kidney function, to Alzheimer’s, cognition and now—mood.

A recent study in the Archives of Internal Medicine compared participants’ long-term mood and cognition when undertaking low-carb and low-fat diets.

A total of 106 overweight and obese participants were randomly assigned to either a low-carb or low-fat diet for one year. Both diets were similar in calories and only moderately energy-restricted, with an average of about 1,400 calories for women and about 1,700 for men.

Mood was checked four times throughout the study year using validated questionnaires and looking at many aspects of mood, including tension, anxiety, depression, dejection, anger, hostility, vigor, fatigue and confusion. Cognitive function was also tested.

And the results:

• Eight weeks into the diet both groups reported similar marked improvement in mood.

• After the initial eight weeks, mood scores started to differ significantly and the low-fat group clearly outperformed the low-carb group in mood scores.

• In the low-fat diet group the majority of mood measures, including the measures for anger, depression and confusion improved long-term and mood was generally better than it was at the beginning of the diet.

• In the low-carb diet group, after an initial improvement in mood the majority of mood measures, including the measures for anger, depression and confusion returned to baseline level (before weight loss), and the positive mood lift was short lived.

• Both groups achieved similar weight-loss results.

• Cognitive functioning tested working memory and speed of processing, and both groups scored similar scores at one year.

Psychological well-being is one of the many health perks one gets from dieting, and at least in this long-term study, the low-carb diet didn’t achieve the sustained elevated mood that the regular low-fat one did.

The authors offer a few hypotheses to explain their finding:

Western diet eating patterns rely on carbs—bread, pasta, rice and fruit are quite central to our cuisine. Low-carb diets are far removed from our normal eating habits, and may create a sense of food preoccupation, social eating impairment and isolation, and may therefore result in a bad mood.

The other explanation is quite intriguing: low-carb diets may change the brain’s chemistry. Low serotonin levels in the brain are known to be linked to depression and anxiety (many antidepressant drugs work by making serotonin more available in the brain). A high-carb diet may increase serotonin production, and a fat- and protein- rich diet may reduce serotonin concentrations in the brain. Therefore, a low-carb (which is also high in protein and fat) diet may decrease serotonin levels and have a negative effect on moods. Serotonin may be only one of the brain chemicals affected by a low-carb diet.

Who is the fairest of them all?

The weight-loss industry is huge—we spend $40 billion a year on weight-loss and diet advice just in the U.S.; the diet business, unlike the American people, is always in great shape.

Each diet boasts its superior results, ease of use and testimonials from happy thin people, exemplifying the most positive outcome possible with no mention of the average results achieved by most dieters, so I think some reality checks are always welcome.

Whenever I see so many products on the market, it’s a clue that maybe none of them has a clear advantage. While all diets that prescribe an energy deficit—fewer calories consumed than calories expended—should work, the problem remains that only five percent of dieters manage to maintain their lower new weight for very long; most dieters typically slowly return to baseline weight in three to five years. In other words—all diets work but actually none of them really does. Our old eating habits are comfortable, and we are prone to fall back on them.

So which is the best diet? You’ll get many different answers and plenty of advice from experts. My point of view isn’t based on personal experience—I don’t diet—but rather on general health advice and common sense: I prefer diets that promote healthy eating habits, moderation, are balanced nutritionally, and resemble habits you can see yourself adopting long-term.

A better diet plan is one that’s both healthy in the long-term and sustainable. The more the weight-loss diet resembles the weight-maintenance diet habits you need to adopt in order to remain at your new weight, the better it is, as acquiring new eating habits is the ultimate challenge.

These general rules of course exclude fad and crash diets, such as the cookie, milkshake and cabbage soup diets, as well as extremely low-calorie diets. Any diet with “miracle” or “easy” label on it should be highly suspect—there are no miracles (sorry!) and losing weight and keeping it off is never easy.

And because losing weight and keeping it off is so difficult, we need to emphasize obesity prevention. Good eating habits, physical activity and a healthy food environment are the best tools to minimize the chances of ever needing to diet.

Dr. Ayala