McCay's hypothesis: undernutrition and longevity

Interaction between physical activity and nutrition early in life and their impact on later development

It has been rare to find studies of the influence of nutrition on growth that have incorporated careful measurements of physical activity. This paper reviews interactions between physical activity and nutrition in early life and finds that such interactions have a significant influence on growth and later metabolism.Young animals are generally characterized by a high level of spontaneous motor activity that contributes to a high rate of energy turnover in early life. Such activity varies greatly between species and individuals and can be increased by reduced (but not extreme) dietary intake especially of protein, with consequent effects on growth rate (slower), body composition (leaner), eventual body size (smaller), lifespan (longer), cardiac resistance to toxic substances (increased) and changes in body lipids. Most studies have been conducted with laboratory rats but the much smaller literature concerning human beings is also reviewed here.In rats, exercise during pregnancy results in offspring that are smaller and leaner and there are later improvements in cardiac microstructure, cardiac resistance to toxic substances and lower plasma cholesterol and triacylglycerol concentrations.In industrialized countries in recent years, children's fitness, especially of the cardiorespiratory system has not developed at the same pace as body size, or has deteriorated, whereas average body mass index (BMI) and the overall prevalence of obesity have increased. This is partly accounted for by reduced levels of physical activity but there is some evidence that higher intakes of dietary proteins in early life are also implicated. Much recent research has focused on the influence of nutrition in the prenatal and early postnatal period on later health. This review has also underlined the importance of exercise and its interaction with diet beginning with the pregnant mother and continuing through childhood. Development and wider use of simple but reliable methods for the evaluation of physical activity and fitness in young children is now an important priority.

Animais gordos e a dissolução da fronteira entre as espécies

Animais de estimação gordos costumavam ser, para muitas pessoas, engraçados e adoráveis; para algumas, os animaizinhos gordos (especialmente gatos) ainda o são: os quadrinhos de Garfield, sobre um gato acima do peso e preguiçoso, venderam bem; há sites e livros dedicados a exaltar a beleza e o encanto dos gatos gordos; e crianças anglófonas são socializadas por meio de livros de leitura fonológicos com títulos como Fat cat on a mat, associando o prazer de ler à fofura de animais de estimação rechonchudos. Tudo isto, no entanto, está mudando. Testemunhamos a transformação da obesidade de animais de estimação de fenômeno trivial ou preferência estética idiossincrática em problema social. Este vem mobilizando os meios de comunicação de massa, a opinião pública e ampla variedade de especialistas, além da intervenção de aparatos de Estado, como os tribunais e a polícia. Este artigo discute as maneiras pelas quais a obesidade ultrapassou a fronteira das espécies. Revisa as provas divulgadas para justificar as cada vez mais comuns - e cada vez mais estridentes - alegações de que estamos em meio a uma "epidemia" de obesidade de animais de estimação (algumas das quais afirmando que os animais de estimação acima do peso chegam a 60% do total), discute a fonte e avalia a credibilidade desta informação. Examina como a obesidade animal é apresentada na mídia por organizações de caridade, como Pet Club UK ou a RSPCA. E oferece reflexões sobre o que a preocupação corrente em relação à obesidade dos animais de estimação pode nos dizer a respeito das dimensões sociais, culturais, médicas, históricas, econômicas, emocionais e subjetivas da obesidade de maneira geral.

A lifetime perspective on foraging and mortality

Food intake carries many potential risks which may impair an animal's reproductive success not only in the current breeding cycle, but also for the rest of its lifetime. We examine the lifetime trade-off between the costs and benefits of food intake by presenting a simple animal foraging model, where each unit of food eaten carries with it a risk of mortality. We show that the optimal food intake rate over an animal's lifetime, for both semelparous and iteroparous animals, is not maximal. Instead, animals are required to strike a balance between the immediate reproductive benefits of gathering food and the future reproductive costs incurred by the food's mortality risk. This balance depends upon the lifespan of the animal as well as the nature of the risk. Different mortality risks are compared and it is shown that a mortality risk per unit time spent foraging is not, in general, equivalent to a mortality risk per unit of food consumed. The results suggest that a mortality risk per unit of food consumed, such as that presented by the presence of a toxin or of a parasite in the diet, has important consequences for feeding behaviour and is a possible factor involved in food intake regulation.

Mitogenic factors accelerate later-age diseases: insulin as a paradigm

Some genes are expressed differently in earlier and later generations of most cell lines. Many diseases become clinically expressed only later in life, and show clustering of the age at onset in the affected siblings, which may be related to the changing expression with age of the genes involved. Because insulin and its receptor are extremely ancient and well preserved structures with almost universal mitogenic effects, insulin may serve a paradigm of this process. It is suggested that by stimulating cell proliferation, hyperinsulinemia speeds up the appearance of later generations of cells with different expression of the genes. Insulin resistance, accompanying any hyperinsulinemia and considered to be a pathogenetic factor of some common later-age diseases, involves only some biochemical, but not mitogenic effects of the hormone. In humans, high levels of insulin in blood are encountered both physiologically after meals and in many pathological conditions: insulin therapy inevitably causes peripheral hyperinsulinemia; in type 2 diabetes hyperinsulinemia precedes hyperglycemia by many years; hyperinsulinemia is an independent risk factor of atherosclerosis, of type 2 diabetes itself, of some forms of dementia and other diseases; obesity is an obligatory hyperinsulinemic condition. The opposite of hyperalimentation, i.e. calorie restriction (at least, in rodents) may exert its life-prolonging effects through decreasing insulinemia and therefore the rate of cell proliferation. Insulin is only one example, and different mitogens regulate proliferation of different cells. It is likely that growth factors in general accelerating the replication of cells, play a role in speeding up the appearance of later-age diseases involving these cells.