Nutrition and growth of suckling black bears (Ursus americanus) during their mothers' winter fast.

In black bears the last 6-8 weeks of gestation and the first 10-12 weeks of lactation occur in winter while the mother is in a dormant state, and reportedly does not eat, drink, urinate or defaecate. Measurements were made of the body composition and organ weights of cubs, of the composition of milk, and of milk intake (by dilution of 2H2O), in the first 3 months after birth. Additional milk samples were collected until 10 months postpartum. Bear cubs were small at birth, only 3.7 g/kg maternal weight, and chemically immature, as indicated by the high concentration of water (840 g/kg) in their bodies. Organ weights at birth were similar to those of puppies. In the first month after birth cubs gained 22 g/d or 0.23 g/g milk consumed; the milk was high in fat (220 g/kg) and low in water (670 g/kg). About 30% of the ingested energy and 51% of the ingested N were retained in the body. Over the entire 12-week period bear cubs required about 11 kg milk, containing (kg) water 7, fat 2.5, protein 0.8 and total sugar 0.25, to achieve a 2.5 kg weight gain. The birth of immature young and the production of high-fat, low-carbohydrate milk seem to be maternal adaptations to limit the utilization of glucogenic substrates during a long fast. Isotope recycling indicates that mothers may also recover most of the water (and perhaps much of the N) exported in milk by ingesting the excreta of the cubs. Lactation represents another aspect of the profound metabolic economy of the fasting bear in its winter den.

Physiological processes of aging: are there special nutritional requirements for elderly people? Do McCay's findings apply to humans?

Aging is characterized by shrinkage of muscle fibers and loss of protein from them. Bone is also lost, and matrix and mineral are lost together. The predominance of breakdown over synthesis is probably the fundamental cause of both muscle and bone loss. Little can be done to prevent this by dietary means, but physical activity is of vital importance in helping to maintain the integrity of both muscle and bone. McCay's finding that rats underfed from weaning lived longer than those that had adequate food has been confirmed by others, but this is only true if the rats remain free of infections and other hazards, particularly during growth. The mechanisms by which underfeeding delays the aging process in rats may apply to the human body but, if so, this is completely offset by other considerations. For their present and future well-being, children should be fed in the best possible way.

Contemporary human diets and their relation to health and growth: overview and conclusions.

Contemporary human diets are probably as diverse now as they have ever been in the history of mankind. The abundance of food in the western world is in stark contrast to the lack of food and near starvation in parts of Africa, the continent where Homo sapiens evolved. The development of agriculture has enabled the population of the world to expand and to colonize almost the whole of its land surface, but the dependence on one staple food has introduced problems. If the staple crop fails, for example because of drought, there may be no alternative, and undernutrition and starvation are the result. Further, if the rest of the diet does not provide the nutrients that the staple food lacks, diseases due to specific nutrient deficiencies become widespread. Vitamin deficiencies among adults are less common now than they were 50 years ago, but even today millions of children in the poor rice-eating areas of the world are blind because their diets were deficient in vitamin A. For physiological reasons infants and young children will suffer most wherever there is a scarcity of food, of water, or of specific nutrients.

The composition of body tissues (II). Fetus to young adult.

The composition of body tissues is a function of the age, nutrition, state of health and physical activity of the individual. In this paper, the effects of age on the composition of healthy tissues are reviewed. Eleven soft tissues (adipose tissue, blood--whole, brain--whole, heart, kidney, liver, lung, muscle--skeletal, placenta, skin and spleen) and cortical bone are considered. Elemental compositions, mass and electron densities are tabulated for the tissues, as a function of age, from fetus to young adult. Although the compositions given here are predominantly for healthy tissues, reported changes because of dietary influences are briefly discussed.

Upper limits of intakes of total fat and polyunsaturated fatty acids in infant formulas.

The upper limit for fat in infant formulas in the United States is 6 g per 100 kcal. This concentration of fat, similar to that of human milk, seems appropriate for fats that are well absorbed. The upper limit for linoleic acid recommended by the working party in the United Kingdom was 1200 mg per 100 kcal. However, there seems to be no evidence that a higher percentage does the infant any temporary or permanent harm.

Effects of suckling and the postsuckling fast on weights of the body and internal organs of harp and hooded seal pups.

The weights of harp seal pups quadruple during 13 days of suckling while hooded seal pups double in weight in a lactation period of just 4 days. Pups of both species then fast for a month or longer. As a first measure of tissue responses to this 'feast and famine' pattern, we weighted the body, sculp (blubber and attached skin), core (carcass including viscera) and major internal organs of seal pups at birth, at the end of suckling, and at the end of the fast. When expressed as a percentage of body weight, the weights of the internal organs of newborn harp and hooded seals were within the range reported for newborn land mammals. During suckling, harp and hooded seals gained 2.3 and 6.5 kg/day body weight, respectively, but a large part (64-73%) of this gain was blubber and skin rather than core. Even though pups were ingesting great quantities of fat, their digestive organs (stomach, small and large intestines, pancreas) were neither particularly large at birth nor did these organs gain in weight or length unusually rapidly. Most organs increased in weight in proportion to the increase in core weight, but the liver and spleen increased proportionately more than the core, and the stomach, heart and kidneys increased proportionately less. At the end of suckling, sculp accounted for more than half of the body weight in both species. The subsequent 4-week fast resulted in weight loss from both the sculp and core, and the liver and spleen decreased in weight by about 70%. The net effect of sequential suckling and fasting was particularly striking in the hooded seal pup, which has a lighter core, heart, liver and spleen at 1 month postpartum than at birth. These data illustrate a remarkable cycle of nutrient deposition and depletion which is undoubtedly central to the survival of young seals in the harsh pack-ice environment.

How much food does man require? An evaluation of human energy needs.

Nutritional individuality is a characteristic of mankind and this is as true of energy intakes and needs as of other attributes. Studies over the years have shown that individuals vary by a factor of two or more in their intakes of energy from the first year after birth to 75 years and over. The metabolic differences that must lie behind this are still not fully understood. Recent ideas about the importance of dietary thermogenesis in energy expenditure seemed as though they might provide an explanation, but not all investigators agree, and the problem has still not been satisfactorily solved. In spite of these individual variations, average intakes and expenditures show predictable changes with age, and males always seem to take more energy than females throughout their lives. This is still true when the intakes are expressed per kg body weight, per square metre surface area and per kg lean body mass. The explanation of this is not certain, but various suggestions have been made. There is evidence that energy intakes, at any rate in the United Kingdom, were falling between the 1950's and 1970's, and this has been attributed to a decrease in physical activity. However, some of the apparent difference is due to the fact that higher factors were used to calculate the energy derived from protein, fat and carbohydrate in the 1930's and 1940's than were used later; if the later factors are applied to the results of the earlier surveys the values for energy are reduced by about 10%. This correction brings the results of the earlier surveys into line with those of the later ones for boys up to 14 years and girls up to 10 years. Older children of both sexes and adults, however, do seem to be eating less than they used to do. The question as to whether women should and do increase their intake of food during pregnancy has been discussed at two previous meetings sponsored by Nestlé. The evidence seems to be that they do not, and it is postulated that metabolic economies enable the women to produce 4 kg of body fat and a foetus weighing 3.5 kg without any increase in energy intake at all.(ABSTRACT TRUNCATED AT 400 WORDS)

Effect of heat on the anaphylactic-sensitising capacity of cows' milk, gots' milk, and various infant formulae fed to guinea-pigs.

Cows' milk--fresh, boiled, and processed in different ways for the domestic market, and various infant milk formulae--was investigated for its sensitising capacity in the guinea-pig after being fed for 37 days. The anaphylactic sensitising capacity was considerably reduced by heat-treatment. As heat becomes more intense and more prolonged so beta-lactoglobulin and casein become less sensitising. It should be stressed that these were results from experiments on guinea-pigs drinking milk. Should they be found to apply to the human infant too, it seems that it would not be impossible to manufacture a non-sensitising but fully nutritive milk product. The sensitising capacity of fresh and boiled goats' milk was examined too, and it was found that boiling reduced the sensitising capacity to an even greater extent than was the case with cows' milk.