Dietary restriction in humans: report on the Little Rock Conference on the value, feasibility, and parameters of a proposed study

Re-adaptation hypothesis: explaining health benefits of caloric restriction

For the effectiveness of under-eating or caloric restriction a simple evolution-based re-adaptation hypothesis is offered. Our ancient ancestors, whose bodies we inherited, ate and weighed a good deal less in relation to their size than we do. Over hundred thousands of years their desire for food was checked by its scarcity and the effort it took to collect it daily from all over the countryside. Thereby they set the reference standard for living and eating normally and healthily, not we. We eat as much as we like. No creature has ever been adapted to that. By practicing caloric restriction and daily exercise, we simulate to some degree the essentials of the way of life of our well adapted forbears. By such re-adaptation to our generic heritage, we re-gain their health at least approximately.

Effect of dietary restriction beyond middle age: accumulation of altered proteins and protein degradation

Dietary restriction (DR) from weaning or young adult stages in rodents throughout their usual life span has been shown to prolong longevity and lower or delay (or both) the occurrence of many late-onset diseases, but the effects of DR when performed at middle age or later have not been well investigated. We have studied the effect of DR initiated late in life on altered proteins and protein degradation. DR initiated in 23.5-month-old mice and continued for 2 months reduced the amount of altered proteins and shortened the half-life of proteins, including oxidatively modified ones. Furthermore, our more recent studies in rats demonstrated that DR initiated later in life (26.5 months old) restored the activities of proteasomes that have been implicated in removal of altered proteins. Thus, DR initiated even relatively late in life appears to have beneficial effects, restoring an animal's youthful condition in terms of the age-related accumulation of altered proteins.

Calorie restriction in biosphere 2: alterations in physiologic, hematologic, hormonal, and biochemical parameters in humans restricted for a 2-year period

Four female and four male crew members, including two of the present authors (R. Walford and T. MacCallum)--seven of the crew being ages 27 to 42 years, and one aged 67 years--were sealed inside Biosphere 2 for two years. During seven eighths of that period they consumed a low-calorie (1750-2100 kcal/d) nutrient-dense diet of vegetables, fruits, nuts, grains, and legumes, with small amounts of dairy, eggs, and meat (approximately 12% calories from protein, approximately 11% from fat, and approximately 77% from complex carbohydrates). They experienced a marked and sustained weight loss of 17 +/- 5%, mostly in the first 8 months. Blood was drawn before entry into Biosphere 2, at many time-points inside it, and four times during the 30 months following exit from it and return to an ad libitum diet. Longitudinal studies of 50 variables on each crew member compared outside and inside values by means of a Bayesian statistical analysis. The data show that physiologic (e.g., body mass index, with a decrease of 19% for men and 13% for women; blood pressure, with a systolic decrease of 25% and a diastolic decrease of 22%), hematologic (e.g., white blood cell count, decreased 31%), hormonal (e.g., insulin, decreased 42%; T3, decreased 19%), biochemical (e.g., blood sugar, decreased 21%; cholesterol, decreased 30%), and a number of additional changes, including values for rT3, cortisol, glycated hemoglobin, plus others, resembled those of rodents or monkeys maintained on a calorie-restricted regime. Significant variations in several substances not hitherto studied in calorie-restricted animals are also reported (e.g., androstenedione, thyroid binding globulin, renin, and transferrin). We conclude that healthy nonobese humans on a low-calorie, nutrient-dense diet show physiologic, hematologic, hormonal, and biochemical changes resembling those of rodents and monkeys on such diets. With regard to the health of humans on such a diet, we observed that despite the selective restriction in calories and marked weight loss, all crew members remained in excellent health and sustained a high level of physical and mental activity throughout the entire 2 years.

Secular growth and its harmful ramifications

Secular growth has been occurring in Europe for about 150 years. In the USA, since 1900, each new generation has increased by an average of 1in (2.54cm) in height and about 10lb (4.54kg) in weight. This trend has generally been viewed as favorable and tallness is admired, with the current ideal height for a man in the Western world being 6ft 2in (188cm). The Japanese have increased in height since the end of the Second World War by about 5in (12.7cm) in height and the Chinese have been growing at the rate of 2.54cm/decade since the 1950s. In spite of admiring greater height, a world population of increasing height and body-weight is a major threat to our environment, health and survival. Based on more than two decades of research, quantitative data are given for increased use of resources, and increased pollution, energy and fiscal costs resulting from a population of larger people. The laws of scaling are described to show why the impact of increasing stature has a non-linear impact on consumption, body-weight, strength, pollution and economic costs. Paleontological findings indicating that larger body size increases the risk of extinction are also discussed. Various studies indicate a loss of 0.47 year of longevity for each cm increment of height. Caloric restricted diets are also reviewed for their applicability to humans. Recommendations are made for dietary practices to moderate growth in our youth and to postpone development of chronic or degenerative diseases.

Calorie restriction in primates: will it work and how will we know?

Dietary caloric restriction is the most robust and reproducible means of slowing aging and extending lifespan and healthspan in short-lived mammals and lower organisms. Numerous aspects of this paradigm have been investigated in laboratories around the world since its inception more than 60 years ago. However, two questions about calorie restriction remain unanswered to this day: (1) By what mechanism does it work? and (2) Will it work in humans? This review will focus on the latter with particular emphasis on evaluation criteria, current studies in primate models, available data, and plans for actual human caloric restriction interventions.

Effects of caloric restriction or augmentation in adult rats: longevity and lesion biomarkers of aging

Caloric restriction (CR) initiated in young rodents has been thoroughly documented to enhance longevity, but its efficacy when introduced at older ages has not been well investigated. Cohorts of 18- and 26-month-old male F344 x BN F1 hybrid rats were fed either: 1) NIH-31 meal (C); 2) vitamin and mineral fortified NIH-31 meal (R); or 3) vitamin and mineral fortified NIH-31 meal supplemented with corn oil and sweetened condensed milk (S). The C control rats were fed ad libitum, R rats were restricted to 32% of the caloric intake of the controls, and S rats were allowed to consume not more than 8% more calories than C rats. After 6 weeks, the average weights were significantly different between all diet and age groups. Although calorie manipulation altered body weight, no significant effect of the dietary intervention on longevity was found. The average lesion burden, including tumor burden and prevalence of nearly all commonly occurring lesions, were comparable between the groups. Thus, the manipulation of weight at ages beyond middle age has a much less profound impact than similar interventions during growth and maturation in rats.

Comparison of the effects of 20 days and 15 months of calorie restriction on male Fischer 344 rats

The aim of this study was to compare, in 19-month-old male Fischer 344 rats, the influence of brief (20 days) and prolonged (approximately 15 months) calorie restriction (CR; consuming approximately 60% of ad libitum, AL, intake) on circulating levels of glucose, insulin, C-peptide, and free fatty acids (FFA); age-matched AL rats were also studied. In the prolonged CR group, there was an approximately 85% decline in fat pad masses (epididymal and retroperitoneal) compared to AL and brief CR rats (these latter groups did not differ significantly). Compared to AL levels, glucose was 15% lower with prolonged CR (p < 0.05) while the brief CR values tended to be lower (10%) than AL; the CR groups did not differ significantly. Plasma FFA levels were significantly (p < 0.05) greater (85-106%) in the brief CR group compared to each of the other groups. Plasma insulin concentrations for the CR groups were lower (p < 0.05; approximately 50-60%) than AL levels. Plasma concentrations of C-peptide (an indicator of insulin secretion) were also lower for each CR group vs AL levels, and a high correlation was found between plasma insulin and C-peptide concentrations (r2 = 0.90; p < 0.001). The C-peptide/insulin ratios for the CR groups were similar, and the value of each CR group exceeded that for the AL rats. These results demonstrate that: the CR-induced reduction in plasma insulin is attributable in large part to reduced insulin secretion; these decreases in insulin secretion and concentration are essentially undiminished when brief CR is initiated rather late in life, and the reductions are independent of substantial reductions in body fat.