Moderate food restriction suppresses the conversion of l-tryptophan to nicotinamide in weaning rats

Abstract

Calorie restriction leads to a change in the metabolism of nutrients. Nicotinamide is biosynthesized from l-tryptophan. We attempted to determine the effects of food restriction on the biosynthesis of nicotinamide from l-tryptophan. Weaning male rats were fed a conventional chemically defined diet without preformed niacin for 63 d. However, the food intake was restricted to 80 and 65% of the intake of the ad libitum-fed control group of rats. The 24-h urine samples were periodically collected, and the urinary excretion of nicotinamide and its catabolites was measured. The conversion percentages were lower in both restricted groups than in the ad libitum-fed control group during the experimental period (control group, 1.37 ± 0.24%; 80%-restricted group, 0.20 ± 0.04%; 65%-restricted group, 0.15 ± 0.02%; control vs. restricted groups, p < 0.01). Food restriction, even at mild level, suppressed the conversion of l-tryptophan to nicotinamide when compared to the ad libitum-fed control group.

Tissue vitamin concentrations are maintained constant by changing the urinary excretion rate of vitamins in rats’ restricted food intake

“…calorie restriction), is commonly performed among people worldwide and is generally referred to as a "diet." Shibata et al 7) reported that mild food restriction reduced tryptophan-nicotinamide conversion, which helps to explain why death secondary to pellagra is pandemic during the "hungry season" which is defined as off-season of food production. In contrast, Shibata et al 1,2,6) reported that severe food restriction increased tryptophan-nicotinamide conversion because the availability of free-type tryptophan increases with body protein breakdown.…”

“…Under ad libitum feeding conditions, these percentages for vitamin B 1 , vitamin B 2 , vitamin B 6 , vitamin B 12 , pantothenic acid, folate, and biotin were about 16, 32, 44, 18, 62, 7, and 23%, respectively. The percentage of excretion of niacin compared with intake of niacin could not be calculated because nicotinamide is biosynthesized from tryptophan, and the conversion percentage is known to be affected by many factors such as energy restriction, 7) starvation, 8) protein intake, 25) and the amino-acid composition. 26) The urinary excretion percentages of vitamins over the intakes were observed some characteristic phenomena.…”

“…6) We found a significantly lower conversion of tryptophan to nicotinamide in rats that underwent food restriction, even mild restriction, than in rats fed ad libitum. 7) In contrast, severe food restriction elevated the conversion of tryptophan to nicotinamide. 8) In the present study, we compared the amounts of B-group vitamins in the liver, kidney, blood, and urine of growing rats that underwent various levels of food intake restriction (80, 40, and 20%) with those of rats fed ad libitum.…”

Vitamin B1 deficiency inhibits the increased conversion of tryptophan to nicotinamide in severe food-restricted rats

“…1) We have also recently found that mild food restriction, which caused a slight increase in the body weight that was not significantly lower than of the free-access control group, significantly decreased the Trp → Nam conversion. 2) In contrast, the Trp → Nam conversion increased in starving rats compared with free-access control rats.…”

“…3) These studies 2,3) imply that food restriction, namely calorie restriction, significantly affects the Trp → Nam conversion process.…”