Diet Versus Exercise in Weight Loss and Maintenance: Focus on Tryptophan

Abstract

An association between mood disturbance, the inability to lose or to stop gaining weight, and a craving for carbohydrates is manifested by many people who are overweight or are becoming so. In a recent study, we observed that low-calorie weight loss diet lowered not only levels of leptin but also levels of essential amino acid tryptophan (TRP) significantly. The disturbed metabolism of TRP might affect biosynthesis of serotonin and could thereby increase the susceptibility for mood disturbances and carbohydrate craving, increasing the cessation probability of weight reduction programs. Alternatively, moderate physical exercise - a potent stimulus to modulate (reduce/normalize) proinflammatory cytokines, which may affect TRP levels - could be helpful in improving mood status and preventing uncontrolled weight gain. In contrast, excessive physical exercise may induce breakdown of TRP when proinflammatory cascades together with TRP-degrading enzyme indoleamine 2,3-dioxygenase-1 are stimulated, which may lead to neuropsychiatric symptoms such as fatigue and low mood.

Keywords: diet; exercise; mood; tryptophan; weight loss maintenance.

Figure 1

Low and very low calorie diet leads to a deficit of essential amino acid tryptophan because of insufficient dietary intake (upper graph), whereas the KYN-to-TRP ratio (lower graph) is not influenced.

Figure 2

Hypothesis of the impact of moderate (upper graph) versus intensive (lower graph) physical exercise on the breakdown of tryptophan and the production of 5-hydroxytryptamine (serotonin) in a healthy individual: Physical exercise evokes a proinflammatory immune response, which is associated with induction of IDO1. In parallel, GCH1 is activated, which leads to the production of BH₄, the necessary cofactor of several amino acid hydroxylases, including tryptophan 5-hydroxylase. In the moderate situation (upper graph), the increase in BH₄ is able to compensate for a possible loss of tryptophan due to IDO1 activity, increased serotonin availability will enhance mood. However, in the situation after prolonged or heavy (= intensive) exercise (lower graph), this is no longer true. High level production of ROS can reduce the life span of BH₄, and athletes may be faced to insufficient supply with serotonin and low mood.