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Health Protocols

Caloric Restriction

Practicing Caloric Restriction with Optimum Nutrition

Although CR has in the past been defined as a 30‒40% reduction in calorie intake (as determined by daily energy expenditure) there is no “official” definition of caloric restriction,94 and newer investigations have revealed CR benefits can still occur at less-restrictive caloric intakes. Based on our current knowledge of CR, its definition may someday be not simply based on a restriction “value,” but rather a combination of anticipated gene expression patterns and physiological changes. As demonstrated in the examples above, CR protocols that have demonstrated significant results over a range of caloric intakes and durations, with and without the inclusion of exercise. Extremely low caloric intakes (only 550 kcal/day) have been used for very short durations (six weeks) with dramatic results in obese individuals, insulin sensitivity increased by 35%; CRP decreased by half, and liver triglycerides decreased by 60%.95,96 However, maintenance of extreme CR for longer periods of time, for instance 45% CR for six months has resulted in several negative side effects including anemia, muscle wasting, neurologic deficits, edema.97 Although the comprehensive CALERIE studies were designed for CR of 16‒25% and have demonstrated short-term success; when compliance is considered, the actual degree of CR in the groups may have been closer to 11.5%.98

The frequency of meals is not important for CR, at least in animal models. Lifespan extensions in rodents have been observed at meal frequencies ranging from six times per day to three times per week.99,100 “Every-other-day-feeding” (EOD), which was initially thought to be distinct from CR, may actually function as a mild CR, and demonstrate a lower incidence of diabetes, lower fasting blood glucose and insulin concentrations.101 It is unclear whether meal frequency affects the benefits of CR in humans. While reduced meal frequency to one meal per day consuming sufficient calories to maintain body weight in healthy, normal-weight, middle-aged adults demonstrated significant increases in blood pressure and LDL-C,102 this effect was not observed in non-obese overweight individuals following an EOD approach to CR.103

The duration of a CR plan depends on its anticipated outcomes. Although controlled longevity data is unavailable for humans, one could imagine that, based on human observational data and the wealth of animal studies, that life extension through CR requires a lifetime commitment. However, reduction in body fat mass, cardiovascular disease and diabetes risks are observable even within the abbreviated timescales of the CALERIE studies (6‒12 months), as are certain markers of slowed aging, such as mitochondrial biogenesis and reduced DNA oxidative damage. Even short (21‒48 day) periods of fasting or caloric/dietary restriction (such as religious fasts) can have favorable effects on blood lipids, insulin sensitivity, and biomarkers of oxidative stress.104,105 Short term CR has also been validated by gene expression data, in which alterations in the expression of age-related genes including those involved in inflammation, apoptosis, and DNA expression could be observed after only four weeks of CR in mice.106

While there is no defined composition of the CR diet, the potentially significant reduction in caloric intake necessitates the consumption of nutrient-dense foods, and the avoidance of “empty” calories from foods such as white flour and refined sugar. It is also imperative that the intake of essential micronutrients, such as vitamins, minerals, essential fatty acids and essential amino acids, are carefully monitored, and added back to the diet if necessary. Even a carefully chosen CR diet may not be nutritionally complete; in studies of four popular, published diet plans that limited calories to 1,100‒1,700 per day including the NIH and American Heart Association-recommended “DASH diet,” all were found to be on average only 43.5% sufficient in RDIs for 27 essential micronutrients values, and deficient in 15 of them.107 While hunger cannot realistically be eliminated during a dedicated CR diet, there are dietary strategies to reduce hunger such as sufficient fiber consumption (increasing fiber intake to 35 grams/day had a significant effect on satiation and adherence to the CR protocol in the CALERIE study)108 and consumption of “fast” proteins, like whey, that are rapidly absorbed and quickly signal satiety.109,110