Low-Fat and Low-Carb Diets’ Effect on Mood

Weight loss can be achieved by restricting calorie intake. This can be in the form of dietary restriction of any one of the three macronutrients found in food: carbohydrates, proteins, fats, or a combination of the three. The present study found that low-fat and low-carbohydrate diets produce similar weight loss and improvement in plasma glucose levels. Low-fat diets improved mood and maintained positive mood better in the long run.

Usually a high-carbohydrate, low-fat, calorie-restricted diet is recommended for weight reduction. But sometimes, a very low-carbohydrate, calorie-restricted diet is also advocated. It is an established fact that in obese individuals, weight loss by dietary modification improves mood. But the results of experiments about low-carb diets are mixed. In young rats it was found that a low-carb diet produced severe cognitive impairment. Short term studies in humans found that a low-carb diet can affect cognitive functions of brain both in a positive or a negative way. This research study reports effects of both a calorie-reduced low-carb diet and a low-fat diet on mood and cognitive functions at one year.

* A total of 118 obese people between 24 and 64 years of age participated. Fifty-seven received an energy-restricted low-carb diet; 61 received a conventional low-fat diet. A qualified dietician designed the diets and also counseled the participants frequently.
* The low-carb group received less than 20 grams per day of carbohydrates for the first eight weeks (with an option to increase to less than 40 g/d afterward). The low-fat group received less than 10 grams/day of saturated fats. Calories provided by both diets was approximately 1,433 calories/day for women and 1,672 calories/day for men.
* The study lasted for 52 weeks. Body weight, mood, working memory and speed of processing, were assessed at baseline and at frequent intervals throughout the study.

* Mean weight loss after 12 months was 30.2 lbs. Plasma glucose level and serum insulin levels decreased significantly. There was no statistically significant difference between these values in the two groups.
* Positive moods increased equally from baseline up to eight weeks in both groups. Thereafter, scores leveled off to baseline for the low-carb group, but remained better for the low-fat group.
* There was significant improvement in memory over time in both groups.
* Speed of mental processing increased up to eight weeks, but returned to baseline after 12 months in both groups.

Next steps/shortcomings
Initially, the low-carb group showed mood improvement, but the effect vanished in the long run. In the Western world, a high-carbohydrate diet is usually prescribed for weight loss. The low-carb group might have faced psychological challenges as the diet prescribed for them was quite different from the more common recommendations for weight control. The present findings are based on obese and otherwise healthy adults with normal mood. Many obese people do suffer from mood disorders like depression. More research is needed before findings can be generalized.

This study shows that both low-fat and low-carb diets are equally effective in weight reduction and improve metabolic parameters. Initially, both diets also improve mood and cognitive performance in similar ways. But mood tends to go back to the baseline level in low-carbohydrate diets by 12 months. Usually a low-carb diet is interpreted by people as a diet low in carbohydrates, with a high fat and protein content. Such a high-fat diet may affect the synthesis of serotonin, a chemical implicated in the psychological functioning of the brain. Overall, a low-fat diet appears better in long-term management of obesity due to the lasting positive effects on mood.

For More Information:
Long-Term Effects of a Very Low-Carbohydrate Diet and a Low-Fat Diet on Mood and Cognitive Function
Publication Journal: Archives of Internal Medicine, (Reprinted) November 2009
By Grant D. Brinkworth, PhD; Jonathan D. Buckley, PhD; Preventative Health National Research Flagship, Commonwealth Scientific and Industrial Research Organisation, and the University of South Australia, Adelaide

*FYI Living Lab Reports Are Summaries of the Original Research.

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