International perspective: basis, need, and application of recommended dietary allowances.

The RDAs emerged in World War II to thwart existing nutrient deficiencies. The RDAs are estimates of need based on the data available. There has been remarkably little change in RDA values. The ongoing revision of the RDAs will introduce new terminology and attempt to recommend values that not only ensure the prevention of nutrient deficiency but that would thwart the more prevalent chronic degenerative diseases as well and recommend upper safe limits for RDA nutrients. The overall goal is to provide estimates of dietary allowances that are intended to avoid preventable illness, including freedom from outright clinical deficiency of truly essential nutrients.

Overview of key nutrients: micronutrient aspects.

Micronutrients are the key to optimal macronutrient metabolism because of their essential role in metabolism. Invariably, metabolic steps require the concomitant involvement of one or more vitamins and minerals. Chronic degenerative disease etiology and rate of pathogenesis are intimately associated with micronutrient imbalances. Although precise mechanisms remain to be identified, antioxidant status is critical in atherosclerosis and cancer pathogenesis. While elucidating estimates and establishing "singular" values by sex and age for parameters such as estimated average requirements, RDA, and RDI, it is imperative to arrive at these estimates in the light of their interdependent role in metabolism.

Recommended dietary allowances for growth, development and performance.

Sufficient scientific evidence has accumulated in our understanding of the impact of the quality of the diet during growth and development to suggest changes in the RDAs. We now recognize that: the quality of the prenatal diet has dramatic impact on growth and development in utero, on birth weight, and on infant mortality and on morbidity during childhood; the diet of the infant, especially during the first three years, has profound effects on the intellectual and physical (work capacity) performance potential during adolescence, and affords a decrease in the probability of morbidity and mortality; the quality of the diet during growth and development throughout adolescence has a life-long potential in the thwarting of chronic degenerative diseases. The implication is a decrease in health care costs and an increase in productivity. Certain limiting nutrient RDAs will need to be updated accordingly.

Human cytoplasmic 3-hydroxy-3-methylglutaryl coenzyme A synthase: expression, purification, and characterization of recombinant wild-type and Cys129 mutant enzymes.

A cDNA for the human cytoplasmic 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) synthase (EC 4.1.3.5) was subcloned and expressed from a T7-based vector in Escherichia coli. The over-produced enzyme was purified using a three-step protocol that generated 20 to 30 mg protein/liter cell culture. The physical and catalytic properties of the recombinant synthase are similar to those reported for the nonrecombinant enzymes from chicken liver [Clinkenbeard et al. (1975a) J. Biol. Chem. 250, 3124-3135] and rat liver [Mehrabian et al. (1986) J. Biol. Chem. 261, 16249-16255]. Mutation of Cys129 to serine or alanine destroys HMG-CoA synthase activity by disrupting the first catalytic step in HMG-CoA synthesis, enzyme acetylation by acetyl coenzyme A. Furthermore, unlike the wild-type enzyme, neither mutant was capable of covalent modification by the beta-lactone inhibitor, L-659,699 [Greenspan et al. (1987) Proc. Natl. Acad. Sci. USA 84, 7488-7492]. Kinetic analysis of the inhibition by L-659,699 revealed that this compound is a potent inhibitor of the recombinant human synthase, with an inhibition constant of 53.7 nM and an inactivation rate constant of 1.06 min-1.

Smokeless tobacco habits and oral mucosal lesions in dental patients.

As part of a smokeless tobacco (ST) intervention study, we collected data on tobacco use habits and oral health for 245 male ST users aged 15 to 77. The study sample was identified during routine dental office visits and represents a relatively diverse population of patients. Oral health data collection included grading the clinical appearance of oral mucosal lesions using Greer and Poulson's classification system, as well as identifying and recording the primary anatomic location of ST placement. Results show that 78.6 percent of ST users had observable oral lesions, 23.6 percent of which were in the most clinically advanced category (degree III). Of the lesions noted, 85 percent were in the same location the patient identified as his primary area of smokeless tobacco placement. In a comparison sample of 223 non-ST-users with the same age distribution, only 6.3 percent had observable lesions. A multiple logistic regression model for ST users showed that lesion presence and severity were most significantly related to current frequency of ST use.

Dietary phenolic compounds: inhibition of Na+-dependent D-glucose uptake in rat intestinal brush border membrane vesicles.

The effects of phenolic compounds on Na+-dependent D-glucose transport were investigated in brush border membrane vesicles isolated from rat small intestine. Screening experiments were conducted with different classes of phenolic compounds in both their native and oxidized forms. Pretreatment of vesicles with tannic acid (1 mg/ml) completely abolished the characteristic overshoot of active glucose accumulation. With chlorogenic acid (1mM), 80% of the glucose transport capacity was lost. Reductions of 30-40% were observed in vesicles treated with catechin, ferulic or caffeic acids. Treatment with gallic acid (1 mM) had little effect. Phenolic oxidation state did not exacerbate the degree of glucose transport inhibition, with the exception of catechol (1 mM), which gave maximal inhibition (86%) in its oxidized form. Gradient-independent glucose uptake was not altered, nor did phenolic treatment increase nonspecific binding of glucose to the membrane vesicles. Possible mechanisms of D-glucose transport inhibition were examined in chlorogenic acid-and tannic acid-treated vesicles. Factors such as alterations in vesicle permeability, size and leakage of transported glucose out of the vesicles were ruled out. Measurements of D-glucose uptake under conditions of Na+ equilibrium suggest that tannic and chlorogenic acids reduce glucose uptake by favoring the dissipation of the Na+ electrochemical gradient, which provides the driving force for active glucose accumulation.

Effects of native and oxidized phenolic compounds on sucrase activity in rat brush border membrane vesicles.

The effects of dietary phenolic compounds on intestinal sucrase were investigated in brush border membrane vesicles purified from rat small intestine. Screening experiments were conducted with different classes of phenolic compounds in both oxidized and native forms. The most potent inhibitor was native tannic acid at 0.1 mg/ml, resulting in an 80% loss of activity. Oxidized tannic acid had no effect. Significant decreases were also observed in vesicles treated with 0.1 mg/ml of catechol or epicatechin, yielding activity losses of 30-50%, regardless of oxidation state. With gallic acid, maximal (40%) inhibition occurred only in the oxidized form. Other phenolic compounds, such as ferulic, p-coumaric and caffeic acids, tended to be slightly inhibitory, while no inhibition was observed with vanillin or chlorogenic acid at the concentrations tested. These results confirm the enzyme inhibitory action of tannic acid, a polyphenolic compound, and also demonstrate that some individual dietary phenolic monomers have the potential to modulate enzyme activity in a brush border membrane vesicle model system.

Priorities in adolescent health care: the teenager's viewpoint.

The purpose of this study was to determine what issues teenagers want discussed or covered when they visit primary care physicians and to assess to what extent such discussion takes place. A questionnaire was administered to 1,564 students aged between 13 and 18 years in six high schools. Mean participant age was 15.3 years; 801 were male and 763 were female. Questions were drawn from both physical and psychosocial aspects of teenage life. The teenagers answered as to whether they would like to discuss the suggested topics on visits to physicians, and whether in fact such a discussion had taken place. The three topics of most interest to teenagers were physical fitness, nutrition, and growth. Teenagers wanted to discuss these topics in over 80 percent of the visits, and they indicated that actual discussion took place in just under 50 percent of the visits. Discussion of sexually transmitted disease was desired by teenagers 70 percent of the time, with a discussion rate of only 18 percent; contraception at 66 percent with a physician discussion rate of only 22 percent. If physicians discuss exercise, nutrition, and growth with teenage patients, in over 80 percent of cases they will be providing the patient with valued information. This initial dialogue will establish a base of communication that may allow for the discussion of issues teenagers often find more difficult (such as contraception, sexually transmitted disease, depression, drugs, and drinking).

Decreased triiodothyronine binding to isolated nuclei from livers of preobese and obese (ob/ob) mice.

L-Triiodothyronine (T3) binding to hepatic nuclei from (ob/ob) mice at different ages was examined and compared with that of lean controls. Results showed a significant reduction in T3 binding in liver nuclei of obese mice at all ages studied. The preobese mice at 2 weeks of age had 27.9% fewer receptor sites/mg DNA compared to lean controls, receptor concentration further decreased to 67.7% at 18 weeks of age. Data presented here demonstrates that the impaired triiodothyronine (T3) binding to hepatic nuclei present in older (ob/ob) obese mice is an antecedent to the obesity. This report also helps to explain the poor thermoregulation and low oxygen consumption present during the preobese phase of the postnatal development of these animals.

Nutrition evaluation of published weight-reducing diets.

The objective of this study was to determine the nutritional adequacy of some of the popular published diet plans. Diet analyses were made using the University of Massachusetts Nutrient Data Bank. Not one of the 11 diets evaluated provided 100% of the U.S. Recommended Daily Allowances for the 13 vitamins and minerals studied. The nutrients most often below recommended levels were thiamin, vitamin B-6, vitamin B-12, calcium, iron, zinc, and magnesium. Vitamin and mineral supplementation may be warranted for individuals following some diet plans.

Food dyes produce minimal effects on locomotor activity and vitamin B-6 levels in postweanling rats.

We investigated the effects of food dye consumption on locomotor activity, brain neurotransmitters, tissue vitamin B-6 levels, and hepatic cytochrome P-450 concentrations in postweanling rats. Animals were individually housed in stabilimeter-type activity cages for 4 1/2 weeks, and fed ad libitum a semipurified basal diet containing graded levels (4, 2, 1, 0.5 or 0%) of a blend of all seven Food, Drug and Cosmetic (FD & C) food dyes. Rats in the 4% dye group were significantly (P less than 0.001) less active during the first 3 weeks of dietary treatment, but no significant differences existed among groups during the final 10 days. Similarly, although dye ingestion depressed food intake (P less than 0.0025) and body weight (P less than 0.05) when averaged for all animals, the differences among groups disappeared by the last week of the experiment. Postmortem tissue analyses revealed no significant effect of dyes on brain tissue levels of serotonin, dopamine, norepinephrine, 5-hydroxyindoleacetic acid or homovanillic acid. Moreover, no significant differences were detected in either plasma and brain tissue levels of pyridoxal phosphate or in hepatic cytochrome P-450 concentrations. These results demonstrate that animals may adapt to the chronic consumption of food dyes and do so with minimal evidence of toxicity. Our data also suggest that previously reported behavioural abnormalities attributed to food dyes are probably unrelated to altered vitamin B-6 metabolism.

Biochemical controls of liver cholesterol biosynthesis.

Major endogenous regulatory controls of cholesterol synthesis including dietary-feedback inhibition, circadian rhythms, feeding/fasting fluctuations, and enterohepatic bile acid circulation are discussed in terms of biochemical control mechanisms of liver cholesterol biosynthesis. Other likely control mechanisms such as cofactors, enzyme levels, and enzyme activities are noted. The current state of the biochemical knowledge is very dependent upon integrated data from one experimental animal - the rat. Inferences and implications in the human are thus limited.

Basic amino acid accumulation in potassium-depleted rat muscle.

In rat muscle, a depletion of potassium is partially compensated for by a gain of sodium. In addition cationic (free basic) amino acids accumulate in the muscle of the potassium-deficient rat. A 31% muscle potassium depletion was induced by dietary restriction of potassium in two groups of rats which differed in the test diet content of lysine and arginine (adequate and excessive). The excess lysine and arginine accumulation in the muscle of the rats fed excess levels of lysine and arginine was accompanied by an equimolar reduction in the gain of sodium. The results demonstrate that lysine and arginine accumulation consists of a transfer of positive charges in compensation to the charges lost with potassium, and that cationic amino acids may spare the role of sodium under these conditions.