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Biomedical subjects

J J Wurtman

Publications and source records attributed to J J Wurtman.

At least 37 records · Page 2Linked to original sources
PubMed1986

Carbohydrate craving, obesity and brain serotonin.

One mechanism through which the brain obtains information about the composition of the diet involves food-induced changes in the plasma amino acid pattern (principally the "plasma tryptophan ratio"), which then cause increases or decreases in brain tryptophan levels, and in the synthesis of a neurotransmitter, serotonin, which is formed from the tryptophan. A carbohydrate-rich, protein-poor meal stimulates insulin secretion; this diminishes plasma levels of the amino acids which compete with tryptophan for transport into the brain (e.g., leucine, isoleucine and valine), thus increasing tryptophan's flux across the blood-brain barrier and its brain levels. In contrast, a high-protein meal contributes so much more of these latter amino acids to the blood stream than of the relatively-scarce tryptophan that it diminishes tryptophan's entry into the brain. This article reviews evidence that the brain actually utilizes the food-induced changes in brain serotonin in order to make choices about what to eat at the next meal. It also discusses the likelihood that a disturbance in this mechanism is involved in producing the "carbohydrate-craving" that is frequently associated with obesity. (This behavior which has been studied by allowing hospitalized subjects to choose freely among isocaloric meals and snacks of varying protein/carbohydrate ratios, typically manifests itself as a propensity to consume 30 per cent or more of the total daily calorie intake in the form of sweet or starchy snacks, usually at a characteristic time of day.) D-Fenfluramine, a drug that selectively enhances serotonin-mediated neurotransmission, also selectively suppresses "carbohydrate-craving" in these subjects.(ABSTRACT TRUNCATED AT 250 WORDS)

Amino Acids↗
PubMed1986

Changes in mood after carbohydrate consumption among obese individuals.

Two groups of obese individuals who consume excessive calories primarily as snack foods have been identified. Carbohydrate cravers consume most or all snacks as carbohydrate-rich foods despite the equal accessibility of protein-rich snacks. Noncarbohydrate cravers consume about equal amounts of protein- and carbohydrate-rich snack foods. Using standardized self-report questionnaires, we measured mood before and 2 h after consumption of a high-carbohydrate lunch (104 g CHO). Responses to the meal differed significantly: noncarbohydrate cravers reported feeling considerably less alert, more fatigued and sleepy, while carbohydrate cravers described little or no change in these aspects of mood. Moreover, noncarbohydrate cravers experienced an increase in depression, while carbohydrate cravers reported feeling less depressed. Findings suggest that snacking habits of obese individuals may be related to subsequent mood states.

Dietary Carbohydrates↗
PubMed1984

Self-selection and regulation of protein: carbohydrate ratio in foods adult rats eat.

When adult rats were offered isocaloric diet pairs, which differed in carbohydrate contents and which contained the same or differing protein contents, the animals chose between the two foods nonrandomly. The overall ratio of protein to carbohydrate consumed was maintained between 0.20 and 0.43, while the range of possible protein:carbohydrate ratios that the animals could have eaten was much broader, i.e., 0.07-3.60. If diet choice was restricted to pairs containing very large proportions of carbohydrate (average wt/wt % of pair greater than 57%), the regulation of the dietary carbohydrate intake was disturbed: much more carbohydrate was eaten, and the protein:carbohydrate ratio was decreased. These observations suggest that there may be an intrinsic requirement for dietary carbohydrate, and that this requirement may be related to the amount of protein concurrently being consumed. The protein:carbohydrate ratio that the animals choose, when allowed the choice, is also the proportion previously shown to produce neither a decrease nor an increase in brain serotonin levels. It is thus possible that the mechanism by which the brain controls nutrient choice involves alterations in serotonin synthesis, causing foods to be selected that will maintain the release of this transmitter at "optimal" levels.

Animals↗
PubMed1984

The involvement of brain serotonin in excessive carbohydrate snacking by obese carbohydrate cravers.

A specific hunger for carbohydrate-rich foods has been observed in animals and human beings and appears to be regulated by the brain neurotransmitter serotonin. Consumption of a carbohydrate-rich meal increases the synthesis and release of brain serotonin (by enhancing the brain uptake of its precursor, tryptophan). As a consequence of this increased release of serotonin, carbohydrate intake is decreased at the next meal. Consumption of protein does not increase brain serotonin levels or decrease carbohydrate intake. A subgroup of obese individuals who consume carbohydrate-rich snack foods at specific times of day or evening has been identified. Such individuals do not routinely snack on protein-rich foods, and their consumption of calories and nutrients at meals is not excessive. Evidence is presented that carbohydrate snacking seems to be related to a "need" to increase the level of brain serotonin; treatment with a drug, d-1 fenfluramine, that increases serotoninergic neurotransmission significantly decreases carbohydrate snack consumption. Weight loss among the population of carbohydrate cravers might be most successful if treatment includes either a diet or drugs that increase brain serotonin activity when the need to snack on carbohydrate is most likely to occur.

Adult↗
PubMed1984

d-Fenfluramine selectively decreases carbohydrate but not protein intake in obese subjects.

Studies on normal rats and on obese human subjects exhibiting 'carbohydrate-craving' suggest that brain mechanisms exist allowing appetites for carbohydrates and proteins to be regulated independent of those for calories and for tastes of the carbohydrates. We observe that virtually all of the excess in daily energy intake among these obese people can be accounted for by carbohydrate snacks, and that a serotonin-releasing drug, d-fenfluramine, selectively diminishes the tendency to consume these snacks.

Animals↗
PubMed1983

The treatment of obesity by carbohydrate deprivation suppresses plasma tryptophan and its ratio to other large neutral amino acids.

We measured plasma concentrations of tryptophan (Trp) and the other large neutral amino acids (LNAA) in 6 control and 7 obese subjects before and after they consumed a low-carbohydrate "protein-sparing modified fast" (PSMF) diet; LNAA levels in control subjects were also assessed after supplemental oral Trp. Consumption of the PSMF diet by non-obese subjects, or obesity per se, caused major reductions in the ratio of the plasma Trp concentration to the summed plasma concentrations of the other LNAA (i.e., the "plasma Trp ratio"), and may thus have diminished brain serotonin synthesis. Administration of even 2 g of supplemental Trp did not elevate the plasma Trp ratio beyond the normal range observed previously in subjects consuming carbohydrate-containing meals.

Adult↗
PubMed1983

Prior carbohydrate consumption affects the amount of carbohydrate that rats choose to eat.

Consumption of protein-rich, carbohydrate-restricted reducing diets has been associated anecdotally with an increased appetite for carbohydrate. We have tested the effect of such a diet on carbohydrate intake by rats. Rats were given either a calorie-restricted ketogenic diet containing protein and fat or a control diet containing carbohydrate along with the protein and fat. When allowed to choose from a pair of isocaloric, isonitrogenous diets containing 25 or 75% dextrin, ketotic rats ate significantly more carbohydrate and total food than control animals during the first 30 minutes of feeding, apparently requiring more of the carbohydrate to obtain an increase in brain tryptophan similar to controls. Ketotic rats ate a significantly higher proportion of total calories as carbohydrate. Similar results were obtained when sucrose replaced dextrin. When ketotic and control rats chose between two diets differing in proportions of fat or protein, no differences were observed between the groups in total food intake nor in the amounts or proportions of fat or protein eaten. We also compared the effects of a small, isocaloric premeal containing only carbohydrate (1.4 g dextrose) or mixed nutrients on subsequent carbohydrate consumption in otherwise untreated rats allowed to choose from 25 and 75% dextrin diets. Rats eating the carbohydrate premeal subsequently ate as much total food as the mixed-nutrient controls, but significantly less carbohydrate. These observations suggest that carbohydrate intake is influenced by prior nutrient consumption and that prolonged deprivation of carbohydrate can lead to overconsumption of this nutrient when it is reintroduced into the diet.

Animals↗
PubMed1979

Sucrose consumption early in life fails to modify the appetite of adult rats for sweet foods.

Male rats consumed a diet containing 0, 12, or 48 percent sucrose on days 16 to 30 of life. Thereafter, they had simultaneous access to all three diets until day 63. No relationship was detected between sucrose consumption early in life and subsequent preference for sucrose. The onset of puberty was associated with a decreased appetite for sucrose among animals of both sexes.

Animals↗
PubMed1979

Free amino acid, protein, and fat contents of breast milk from Guatemalan mothers consuming a corn-based diet.

Diet compositions and breast milk levels of free amino acids, protein, and lipid were compared in lactating American and Guatemalan women. The protein in the American diet derived principally from animal sources, whereas that in the Guatemalan diet was based most exclusively on cereal grains and legumes. Corn, in the form of cornmeal, was the predominant food. Because of these dietary differences, the Guatemalan women consumed significantly smaller amounts of protein than the American women. The concentrations of most of the free amino acids in aliquots of breast milk from the Guatemalan women were lower than those in samples from the American women. In particular, tryptophan and lysine levels were 23% and 29%, respectively, of the levels in the American breast milk samples. The Guatemalan samples contained less protein, and, when values from Guatemalan women who had nursed only for 6 mth or less were considered, the fat content was also less than in the American samples. The lipid content of the milk, however, did not differ between the two groups when the length of the lactation period was not controlled. The substantial cultural differences between the two groups in the frequency and duration of nursing probably prevented the identification of a clear dietary influence on milk lipid content. The correlations found between diet composition and either the amount of protein or the levels of free amino acids in breast milk suggest that, if a mother's diet is deficient in high-quality protein, the deficiency may be reflected in the composition of her milk, perhaps to the detriment of the nursing infant.

Amino Acids↗
PubMed1977

Fenfluramine and fluoxetine spare protein consumption while suppressing caloric intake by rats.

The effects of fenfluramine and other sanorectic drugs on the consumption of both protein and total calories by rats given simultaneous access to two isocaloric diets containing 5 or 45 percent casein were examined. Anorectic doses of fenfluramine failed to decrease protein intake but increased the proportion of total dietary calories represented by protein. In contrast, anorectic doses of d-amphetamine decreased protein and calorie consumption proportionately. Subanorectic doses of fenfluramine also increased the proportion of caloric intake represented by protein among animals given prior treatment with the serotonin precursor tryptophan. Fluoxetine, a drug that blocks reuptake of serotonin, similarly spared protein consumption while reducing caloric intake. These observations indicate that two distinct brain mechanisms, sensitive to different drugs, underlie the elective consumption of protein and calories.

Animals↗