Effect of High-Fat Diet on Thermal Acclimation With Special Reference to Thyroid Activity

Abstract

In an attempt to clarify why the seasonal variation of basal metabolic rate (BMR) of Japanese is different from that of Caucasians (white American and Canadian), animal experiments were performed to clarify the effect of dietary composition on thyroid activity, metabolic adaptation to heat, and tolerance to cold, using groups of rats

Effects of Diets on Cold Tolerance and Metabolic Responses to Cold in Fasted Rats

“…In the present study the blood ketone body concentration in the fasted cold-acclimated rats was also lowest among three groups at 25•Ž( et al,1974;OHNO et al,1975 YASUMOTO and SASAKI,1969;YOSHIMURA et al,1972),although protein turnover is enhanced in cold acclimation (YOUSEF and LUICK,1969;YOUSEF and CHAFFEE,1970)and survival time in the cold is reduced in the fasting rats fed a low-protein diet (BEATON et al,1964).The present results confirmed that the find-T.OHNO ings by SASAKI et al(1969)and YOSHIMURA et al(1972were also the case in the fasted animals as to not only cold tolerance assessed by the fall in colonic temperature but the metabolic responses of energy yielding substrates to cold.Judging from these results,we might say that there exists a certain amount of protein content in the diet is required for the normal cold tolerance and excess intake of protein over this range will not further improve cold tolerance, either in the fed or fast state.…”

“…However,we have previously reported that a high-fat diet does not improve cold tolerance in fed rats (KUROSHIMA et al,1974)and suggested that the lack of effect of a high-fat diet in the cold is attributable to a decreased activity of sympathetic nerves (KUROSHIMA et al,1974)and of thyroid gland (KUROSHIMA et al,1971).On the contrary,YOSHIMURA et al (1972)claimed that a high-fat diet improved cold tolerance,possibly due to an activation of thyroid function,in the fed state.The difference between the work by YOSHIMURA et al(1972)and ours (KUROSHIMA et al,1974)led us to consider the effect of high-fat diet on cold tolerance under different experimental conditions such as the fast state where certain metabolic challenges occur.Precise mechanisms involved in the beneficial effect of high-fat diets observed in the present study remain to be studied.However,it should be noted that less increase in blood FFA and less decrease in blood glucose were seen in the animals exposed to cold on highfat diets.When the blood concentrations of these metabolites in animals exposed to cold were plotted against the fall of colonic temperatures,there was a significant negative correlation for glucose and a positive correlation for FFA (Figs.3 and 4). and YOUNG,1959;SCOTT and ENGEL,1953) and an elevating action of high-fat diet on blood ketone bodies (OHNO et al,1975).…”

“…A number of studies have been made of the effect of diet composition on cold tolerance,but the results have been rather conflicting.Evidence in favor of a fatty diet came at first from studies in rats by LEBLANC(1957)and by MITCHELL et al(1946)in man,demonstrating slower and lower fall of rectal temperature in the cold as a result of high-fat diet compared to standard control diet.However, some investigators have claimed that a diet high in fat is not necessarily beneficial to resistance to and growth in the cold (BOBEK and GINTER,1966;GIAJA and GELI-NEO,1934;LANG and CRAB,1944).As to the mechanism involved in a favorable effect of a high-fat diet in relation to cold acclimation and resistance,development of certain metabolic changes has been suggested by the observations that the animals on high-fat diets have persistently higher oxygen consumption on an acute or long-term exposure to cold (Ito et al,1968;SASAKI et al,1969;YOSHIMURA et al,1969). Further,YOSHIMURA et al(1972)reported a superiority of high-fat diets in cold acclimation mediated by accelerated thyroidal activity,whereas KURO-SHIMA et al(1971)contended that the effect on the thyroidal function was rather suppressive.Recently,the authors (KUROSHIMA et al,1974)showed that the rats on a high-fat diet excretedless vanilmandelic acid in the urine and did not exhibit any augmented cold resistance in the fed state,although they showed certain metabolic changes.An elevated energy metabolism during cold acclimation has been ascribed to an increased lipid metabolism (MAsoRo,1966)and,in addition,, partly to an enhanced protein turnover (YOUSEF and LUICK,1969;YOUSEF and CHAFFEE,1970).In relation to the effect of protein in the cold,a low-protein diet has been described as decreasing the survival time during starvation in the cold (BEATON et al,1964),while cold tolerance has been shown to be similar in rats on a high-protein diet to that in rats on a normal standard diet in the fed state (YASUMOTO and SASAKI,1969).…”

Loss of Weight, Sodium and Water in Obese Persons Consuming a High- or Low-Carbohydrate Diet

“…Information sup porting the accuracy of this assumption has come from animal experiments [35] and studies on healthy persons [29,30]. It is con ceivable that a definitive clarification of this moot point could be achieved by means of a methodologically laborious approach involv ing the determination of the body composi tion.…”

Comparative Studies in Obese Subjects Fed Carbohydrate-Restricted and High Carbohydrate 1,000-Calorie Formula Diets

“…Whether there actually is a diminution of the glycogen stores over a period of 13-78 days under the described experimental conditions, sufficient to explain mean daily weight variations of as much as 64 g, cannot be decided on the basis of the data published in the literature relative to the behavior of the glycogen stores (6,8). The suggested operation of an effect which raises the metabolic rate (7) receives further support from investigations on experimental animals (18) in which an increase in oxygen uptake and thermogenesis had been observed on a high-fat diet, but not on a highcarbohydrate diet. Studies on normal-weight individuals ingesting a diet restricted in carbohydrate and high in fat likewise demonstrated an increased energy expenditure (16).…”