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Low Fat Intake Sweetens Dieters' Mood

Posted: Monday, November 23, 2009

Restricting fat rather than carbohydrate intake may make dieting easier on the mood, researchers found.

Despite the same victories on the scale, dieters who stuck to low fat consumption had lasting reductions in hostility, confusion, depression, and overall bad mood scores during one year of dieting compared with those on a low-carb diet (P<0.05), in a randomized weight loss trial.

These findings provide yet another reason to go with the low-fat, high-carb, calorie-restricted diet recommended by the American Dietetic Association and others, said investigators led by Grant D. Brinkworth, PhD, of the Commonwealth Scientific and Industrial Research Organisation-Food and Nutritional Sciences in Adelaide, Australia.

Weight loss itself has consistently been shown to improve mood, but whether one diet or another is better for psychological state has yielded inconclusive results. 

So Brinkworth's group analyzed mood and cognitive effects in a weight loss trial that randomized 106 overweight and obese adults (mean BMI 33.7 kg/m2) to an energy-restricted diet that provided 1,433 to 1,672 kcal through one of two strategies:

    * A low-fat, high-carbohydrate diet comprised of 46% of total energy from carbohydrates, 24% from protein, and 30% from total fat (less than 8% saturated fat).
    * A low-carbohydrate, high-fat diet with the goal of 4% of total energy from carbohydrates, 35% from protein, and 61% from fat (20% saturated fat).

To achieve these targets, participants met one-on-one with a dietitian at least monthly through the one year study. They were given meal plans and recipes along with a supply of key foods for about 30% of their total energy consumption for the first eight weeks and $40 food vouchers at each visit to the dietitian thereafter.

Both groups achieved substantial weight loss over one year, averaging 13.7 kg (30.2 pounds) without a difference between groups (P=0.26 for interaction). Glucose and insulin level changes were also similar between groups (P=0.79 and P=0.75, respectively).

Both groups also had similar improvements in mood and well-being as measured by the Profile of Mood States, Beck Depression Inventory, and Spielberger State Anxiety Inventory scores over the first eight weeks.

But thereafter, mood scores rebounded in the low-carb group only, such that the change over time was significantly different for anxiety, total mood disturbance, and anger/hostility, confusion/bewilderment, and depression/dejection subscales (P<0.05 for interaction).

At week 52, a post hoc analysis showed significantly better scores for the low-fat diet compared with low-carb diet for anger/hostility (P=0.006), confusion/bewilderment (P=0.02), and depression/dejection (P=0.05) subscales as well as overall mood (P=0.001).

The differences between groups had medium effect sizes of 0.5 to 0.7, which the researchers said are clinically relevant, though averages remained within the normal range for healthy adults in both groups.

The results suggested "that some aspects of the low-carbohydrate diet may have had detrimental effects on mood that, over the term of one year, negated any positive effects of weight loss," they wrote.

Because the low-carb diet is so far removed from typical Western food habits, it "may have created a significant challenge for participants, leading to the possibility of food preoccupation, social eating impairment, and dysphoria," they posited.

But serotonin and neurotrophic factors could contribute as well, Brinkworth's group noted.

Both groups also showed an initial improvement in working memory that didn't disappear over time. Neither memory nor mental processing speed appeared affected by diet composition, though the researchers noted that cognitive function may be affected in other, unmeasured respects, such as attention and short-term memory.

Source: Diabetes In Control: Brinkworth GD, et al "Long-term effects of a very low-carbohydrate diet and a low-fat diet on mood and cognitive function" Arch Intern Med Nov 9, 2009; 169: 1873-80.

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