Recent activities of public agencies to assure healthful diets for Americans.

In the United States, public agencies long have been involved in providing information about food and nutrition. Over the years, however, the nature of that involvement has shifted. Initially the emphasis was on practical information about agriculture and home economics. Gradually emphasis has shifted to concerns about malnutrition and, more recently, to concerns about overconsumption and associated health problems. This paper reviews some of the food and nutrition-related activities of public agencies and summarizes some recent concerns related to nutrition "recommendations", "goals", and "guidelines". Two key publications related to nutrition issues are: 1) "Nutrition and Your Health: Dietary Guidelines for Americans," published jointly by United States Department of Agriculture and Department of Health and Human Services and 2) "Toward Healthful Diets," from the Food and Nutrition Board of the National Academy of Sciences. One of the guidelines in the former publication tends to encourage the dairy industry to orient toward reducing consumption of milk fat. In contrast, the analysis in the latter publication tends to encourage adoption of an approach to promote nutrition education and marketing programs without necessarily reducing consumption of milk fat. The approach of dairy industry would differ depending upon which guidelines were adopted.

Digestibility and effects of whole cottonseed fed to lactating cows.

Four lactating Holstein cows producing about 21 kg milk/day were fed complete rations containing 0, 5, 15, and 25% whole cottonseed in a 4 X 4 Latin square design. Diets were fed ad libitum. Periods were 21 days in length with total collections of feces and urine during the last 7 days of each period. Digestibilities o nitrogen, lipid, and energy increased with increasing cottonseed in the diet. There were no significant effects of cottonseed on digestibility or availability of fiber components, calcium, phosphorous, and magnesium. Cottonseed feeding did not affect dry matter intake or milk yield but did increase yields of milk fat and fat-corrected milk and decrease milk protein and solids-not-fat percentages. Synthesis of fatty acid in the mammary gland was depressed by about 50% on the 25% cottonseed diet, but transfer of dietary fat resulted in twofold increases in yields of stearic and oleic acids. Hydrogenation of cottonseed fatty acid in the rumen resulted in a fourfold increase in yield of trans oleic acid in milk fat. Samples from bulk milk tank and data collected from 55 commercial dairies showed similar changes in fatty acid composition of milk from cows fed whole cottonseed. There was no apparent effect of feeding up to 2.9 kg cottonseed dry matter per cow per day on calving interval or on incidence of displaced abomasum, ketosis, milk, fever, or retained placenta.

Influence of sampling on fatty acid composition of human milk.

To study effects of sampling on the fat and fatty acid composition of human milk, three subjects each obtained four complete expressions of milk in sequential fractions from each breast. Two subjects collected partial expressions of about 5 ml of milk from each breast frequently over a 2-mont period. Milk samples were analyzed gravimetrically for fat and by gas chromatography for the fatty acids 10:0, 12:0, 14:0, 14:1, 16:0, 16:1, 18:0, 18:1, and 18:2. While hindmilk contained a higher percentage of fat than foremilk, fatty acid composition of the milk fat did not vary throughout a nursing. Fatty acid composition from pairs of left and right breast samples collected at the same nursing did not differ. Therefore, fatty acid analyses of human milk will be representative of the entire nursing if the sample is taken from either breast at any time during the nursing.

Fatty acid composition of prepared infant formulas.

The fatty acid composition of eight American, eight European, and four Japanese prepared infant formulas were determined and compared with fat sources listed on labels. Unsaturated fatty acids ranged from 20 to 83 per cent of the total. Generally, the fatty acid composition was consistent with the types of ingredients used; those with corn or soy oil had the highest levels of unsaturated fat, and those with milk fat the lowest; formulas of mixed composition fell in between. The formulas were compared with values for the fatty acid composition of human milk in the literature.

Effects of feeding protected tallow on composition of milk and milk fat.

Official methods were used to analyze composite samples of milk collected during the first 15 wk of lactation from 21 Holstein cows fed a milled ration containing 0 (basal), 15% (medium, or 30% (high) protected-tallow supplement (seven cows per treatment). Protein fractions and amino acid composition of the total proteins were determined from samples of individual milking. Melting characteristics of pooled samples were determined by nuclear magnetic resonance. Milk yield was similar for the three treatments, but percent fat and fat yield were higher for cows fed protected tallow. Percentages and yields of protein and solids-not-fat were decreased on the protected tallow treatments, especially for high tallow. The decrease in protein was in the casein fraction. Amino acid composition of the total proteins was similar for the three treatments. Feeding protected tallow caused decreases in all fatty acids except 4:0, 16:1, 18:0, and 18:1 which increased. Nuclear magnetic resonance indicated that butter from the basal group would be harder than that from cows fed protected tallow.

Influence of diet on trans fatty acids in human milk.

In two experiments on relations between diet and milk lipids, subjects recorded food intake for 1 week and saved duplicate portions of foods consumed on 3 days. Diet collections were analyzed for selected nutrients and percent fatty acids. In the first experiment, for 1 week five subjects took morning and evening milk samples for fatty acid analysis. Significant differences were found in percentages of trans- 18:1 and total trans fatty acids between subjects' milks but not between morning and evening samples. In the second experiment six additional subjects collected milk samples in the morning only. Subjects were significantly different in the percentages of trans- 18:1 and total trans acids in their milks. In nine of the 11 subjects the fluctuation of percent total trans acids in the milk appeared to follow dietary trans changes after a 12 to 36 hr lag period. A significant correlation was found for diet and evening milk of the same day. Polyunsaturated/saturated ratios of the fatty acids in the diet lipids were related to those for milk lipids from the same evening and the next morning. Although other factors are involved, diet lipids influence trans fatty acids and polyunsaturated/saturated ratios of the fatty acids in human milk.

Plasma lipid changes in young adult couples consuming polyunsaturated meats and dairy products.

Twenty-five young couples consumed either a saturated or polyunsaturated fat diet for a 20-week period. The polyunsaturated beef, lamb and dairy products, high in linoleic acid, were produced by feeding ruminant animals "protected lipid" feeds which prevent hydrogenation of fats in the rumen. The experimental design provided for four dietary groups: A) saturated diet for 20 weeks; B) polyunsaturated diet for 20 weeks; C) saturated diet for 10 weeks then polyunsaturated diet for 10 weeks; and D) polyunsaturated for 10 weeks then saturated diet for 10 weeks. Polyunsaturated-to-saturated ratios (linoleic: total saturated fatty acids) for the diets were: prestudy, 0.43-0.56; saturated 0.11-0.14; polyunsaturated, 0.56-0.62. Factors other than diet that appeared to affect cholesterol responses were carefully considered. During the initial 3 weeks (regimentation period) plasma cholesterol concentration decreased in all groups irrespective of diet. This was followed by two experimental periods in which the effects of the prescribed diets were readily apparent (response periods I and II). The final 4 weeks of the study were characterized by diminishing compliance with the dietary discipline (abatement period). Subjects in each group (A,B,C,D) were subdivided into high and low on a basis of each group's initial median cholesterol level. Those in the high subgroups were very responsive to dietary changes whereas those in the low subgroups were not. Combined responses of high subjects were: polyunsaturated diet, -10.7 mg/dl (P less than 0.025), saturated diet, d8 mg/dl (P less than 0.05). Combined difference between saturated and polyunsaturated diets was 18.5 mg/dl or approximately a 10% cholesterol difference between the experimental polyunsaturated and saturated diets.

Ascorbic acid and copper in linoleate oxidation. I. Measurement of oxidation by ultraviolet spectrophotometry and the thiobarbituric acid test.

The UV absorption method and the thiobarbituric acid (TBA) test for oxidation of an aqueous suspension of linoleate were compared. The absorption method depends on the formation of hydroperoxides having conjugated double bonds that absorb strongly at 233 nm. The absorption at 233 nm increased markedly during oxidation of linoleate catalyzed by either ascorbic acid or cupric ions. The concentration of ascorbic acid in the reaction mixture was also measured by UV absorption at 265 nm and pH 7.0. Color development in the TBA test also increased markedly with the extent of oxidation of linoleate. When ascorbic acid was the catalyst, UV absorption detected early stages of oxidation with greater sensitivity than the TBA test. The reverse was true when Cu(++) was the catalyst. In general, the relation between the two procedures will depend on whether copper is present when the TBA test is made.

Ascorbic acid and copper in linoleate oxidation. II. Ascorbic acid and copper as oxidation catalysts.

Both ascorbic acid and copper were strong prooxidants in the oxidation of linoleate in a buffered (pH 7.0) aqueous dispersion at 37 degrees C. Minimum concentrations at which catalytic activity was detected were 1.3 x 10(-7) m for copper and 1.8 x 10(-6) m for ascorbic acid. For concentrations up to 10(-3) m, the increase in rate of oxidation with increase in concentration of catalyst was greater for ascorbic acid than for copper. Ascorbic acid had maximum catalytic activity at 2.0 x 10(-3) m, but was still prooxidant at the highest concentration tested (5.0 x 10(-2) m). Dehydroascorbic acid was a weaker prooxidant than ascorbic acid. Further degradation products of ascorbic acid were not prooxidant. In early stages of the oxidation autocatalytic behavior was observed with copper, but not with ascorbic acid. Ascorbic acid functioned as a true catalyst, i.e., it accelerated the reaction but it was not oxidized simultaneously with the linoleate. It is proposed that the dehydroascorbic acid radical initiates the linoleate oxidation reaction.

Ascorbic acid and copper in linoleate oxidation. 3. Catalysts in combination.

In promoting oxidation of 0.02 m potassium linoleate in a buffered (pH 7.0) aqueous dispersion at 37 degrees C, ascorbic acid at low concentrations (1.8 x 10(-6) and 1.8 x 10(-5) m) in combination with copper (1.3 x 10(-7) to 1.3 x 10(-3) m) had greater catalytic activity than the additive activity of the two catalysts individually. Possible explanations for the enhanced catalysis include reduction of copper by ascorbic acid to the cuprous form, increased concentration of semidehydroascorbic acid radical, and formation of a metal-ascorbic acid-oxygen complex. Some combinations of ascorbic acid (1.8 x 10(-4) and 1.8 x 10(-3) m) and copper (1.3 x 10(-6) and 1.3 x 10(-3) m) inhibited the formation of conjugated dienes but not the oxidation of ascorbic acid, and caused rapid loss of part of the conjugated dienes that were already present. It is suggested that free-radical inhibitors formed by the combination of catalysts inhibit initiation of lipid oxidation but not copper-catalyzed oxidation of ascorbic acid. Effects of the inhibitory combinations on changes in UV absorption by conjugated dienes, and absorbance in the TBA test, indicate the presence of at least two conjugated dienes that differ in stability.