David L. Trout

Vitamin C and cardiovascular risk factors.

The concept that ascorbic acid (vitamin C) supplementation protects against coronary heart disease developed in the late 1970s when vitamin C intakes in industrialized nations were lower than at present. Supplementation was then shown to lower plasma total cholesterol and, among some elderly men, to raise high-density lipoprotein cholesterol. However, among people in initially good vitamin C nutriture, these effects are usually not seen. In five populations of essentially healthy people, blood pressure has been found to correlate negatively with vitamin C status. Recently, in a placebo-controlled, double-blinded study, extra ascorbic acid for 6 wk was observed to lower systolic and pulse pressure in a small group of borderline hypertensive subjects.

BLOOD PRESSURE AND PLASMA LIPIDS DURING ASCORBIC ACID SUPPLEMENTATION IN BORDERLINE HYPERTENSIVE AND NORMOTENSIVE ADULTS

Abstract In order to clarify the relationship of vitamin C to hypertension, a tablet of 1000 mg ascorbic acid (AA) or a placebo was supplied daily to 20 adult subjects for two 6-week periods in a randomized, crossover design. The subjects consumed self-selected diets and were in good vitamin C status; and 12 were classified as borderline hypertensive. AA supplementation reduced systolic blood pressure and pulse pressure but did not affect diastolic blood pressure. Total plasma cholesterol, high density lipoprotein cholesterol and total triglyceride were not affected. It appears that vitamin C supplementation may have therapeutic value in human hypertensive disease.

The Amount and Distribution of Water, Dry Matter, and Sugars in the Digestive Tract of Rats Fed Xanthan Gum

Abstract Diets containing a nutritionally adequate, high-maltose nutrient mixture and either 4% xanthan gum or 4% cellulose were fed ad libitum to rats. The feeding of this gum increased the combined weight of the small intestine and its contents by 110%. This effect was partially due to an enlarged intestinal cell mass and to extra dry matter in the contents but chiefly to a 400% increase in intraluminal water. Xanthan feeding enhanced greatly the persistence of sugars beyond the proximal quarter of the small intestine and increased their total recovery in the first three quarters of that organ by 150%. The xanthan-induced increase in intraluminal water in the small intestine was partially due to a slowed absorption of osmotically active substances from the gut.

Atypically high insulin responses to some foods relate to sugars and satiety

Much research has focused on how the glycemic index (GI) of the diets of healthy people relates to long-term risk for coronary heart disease, stroke, and non-insulin dependent diabetes. Low-GI diets appear to produce some of their beneficial effects largely by moderating insulinemic responses to meals. Wolever and Bolognesi (1996) have derived a formula for predicting the insulinemic index (II) from the GI for starchy foods. Using data from Holt et al. (1995, 1997) on a wide variety of common foods, we have examined differences between the observed II and GI-based estimates of the II. These differences were found to correlate negatively with satiety index ratings and positively with contents of total sugars. We suggest that the aforementioned method of measuring and expressing the relation between the GI and the II may prove useful in exploring how various components and sensory properties of food may affect hunger and energy intake.

CIRCADIAN VARIATION IN THE GASTRIC-EMPTYING RESPONSE TO EATING IN RATS PREVIOUSLY FED ONCE OR TWICE DAILY

Four experiments dealt with circadian variation in the gastric emptying (GE) response to eating, among rats accustomed to eating once (1x) or twice daily (2x). In measuring GE response, a test meal [10 g accustomed diet per (kg body weight)3/4] was fed close to a scheduled eating time or after a delay of up to 24 h. GE response was the fraction of the ingested test meal emptied per hr, up to a known degree of emptying, e.g., 50-58% of the test meal. Animals accustomed to the prescribed eating patterns ate promptly and at similarly rapid rates at all times of day. GE response, as plotted against time of response, fit a 24-h cosine model. Acrophase (time of maximum GE response of the fitted model) was similar, being 1.5 and 2.1 h, respectively, after the starting time of the accustomed dark-span meal for 1x and 2x rats, while amplitude (1/2 the maximum-to-minimum difference) was 41 and 24% of the MESOR (rhythm-adjusted mean). Characteristics of the GE rhythm appeared to be unchanged among 1x rats, severely versus minimally restricted in food intake during a final 9 days.

Prediction of glycemic index among high-sugar, low-starch foods

A weighted mean of the glycemic index (GI) values of the constituent sugars of a non-starchy fruit is known to give a rough estimate of the GI of that fruit. Previously observed GI values (GIob) were, on average, lower than the calculated GI of the sugar mixture (GIsm) for nine acidic fruits (pH of 3.24-4.17) and tended to exceed the GIsm for six near-neutral non-starchy foods (pH < 5.33). A formula for predicting GI from GIsm and food pH was developed, and it accounted for 69% of the sum of squares for the 15 GIob values. A model that proposed that organic acids and their acidic anions slow gastric emptying and thereby lower GI was developed, and it was found to account for 57% of the GIob sum of squares. The substances responsible for lowering GI in acid fruits and the mechanisms of their action remain to be identified.

Intraintestinal Carbohydrate in Rats during the Feeding of Glucose or of Raw or Cooked Cornstarch

Abstract The quantity of free and total (measured after hydrolysis) glucose in the small intestine was examined in rats during a daily period of high food intake. In experiment 1, rats were fed a high-glucose diet, and intestinal contents for analysis were collected by several procedures, all of which yielded similar results. In experiment 2, nutritionally adequate diets containing 66.9% carbohydrate as glucose or cooked (pregelatinized) or raw cornstarch were fed ad libitum for 13 days. The small intestine then contained 37 and 40.6 mg free and total glucose, respectively, in glucose-fed rats, similar amounts of both components in animals fed the cooked starch, and 600+% more total glucose in rats fed raw cornstarch than glucose. In all three dietary groups, total glucose content of the intestine was positively correlated with dry matter content of the stomach.

Effect of Exercise and Dietary Carbohydrate on Glucose Oxidation in Rats

Summary The effect of high-fat vs high-carbohydrate diets on the relative role of the pentose cycle (PC) in glucose catabolism was studied in exercised and sedentary rats fed different carbohydrate sources. Expired 14CO2 was measured after injection of 14C-glucose labeled at C-1 or C-6 or at all carbons, and data were fitted to an experimental model. Ad libitum fed Sprague-Dawley rats appeared to show a diurnal rhythm in the degree of utilization of the PC in glucose catabolism. Exercise of calorically restricted animals reduced the relative role of the PC; but altering the fat:carbohydrate ratio of the diet of ad libitum fed animals had no apparent effect. Under a variety of conditions, at least 25% of the glucose which entered relatively labile pools was selectively decar-boxylated at the C-1 position.

Rates of Net Absorption of Fat when Fed Alone or with Essential Nutrients

Summary The net rate of fat absorption, following a test meal of olive oil, was found to be 3.9 g/24 hr/250 g rat. When WR-1339 (800 mg/kg) was injected iv into rats similarly fed olive oil, fatty acids were found to accumulate in the blood plasma at a similar rate. These rates, however, were 30% lower than that observed during prolonged ad libitum consumption of a high-fat diet and were almost 50% lower than that found among fasted rats when fed the same high-fat diet.