Nutrition: Calorie Reduction's Influence on Healthy Aging
For centuries humans have been fascinated by the idea of a "fountain of youth" or some magic bullet to ward off the realities of aging. Worldwide, attempts have made to increase lifespan and prevent the chronic diseases associated with aging. In response to this demand for more information on ways to prolong life, researchers have studied the effects of manipulating calorie intake via calorie restriction (CR), intermittent fasting, and periodic dietary restrictions. This leads to several questions: How important are body weight and energy consumption to healthy aging and the promotion of optimal health? Does controlling weight and calorie intake help stave off chronic disease and promote longevity? If so, as a practitioner, how can you help your patients live a long life?
This article will review the pros and cons of CR and low body weight as they relate to chronic disease, aging, and longevity. It will also review the use and efficacy of these techniques during the latter years of life.
Nutrition in Aging
For years, studies done on laboratory rats and mice have found that subjects live up to 40% longer than usual and are more resistant to age-related diseases when they are fed a diet with at least 30% fewer calories than the norm.3 More recent research conducted on rhesus monkeys has shown promise that CR without malnutrition results in reduced disease and increased longevity among primates.4
Some limited research has been conducted in humans, and more is underway. In 2015, Ravussin et al, in the Journals of Gerontology, Series A, showed CR to be protective against abdominal obesity, diabetes, hypertension, and cardiovascular disease and to reduce hormonal and metabolic factors associated with increased cancer risk. Furthermore, CR may reverse age-related autonomic decline and improve memory in the elderly.5,6
Metabolic and physiological studies of a group of self-imposed CR members have been conducted over an average of 6.5 years. This group consists of lean volunteers with an average consumption of 1,800 kcal/day (approximately 30% fewer calories than age- and sex-matched volunteers consuming a typical Western diet). The CR members consume a diet rich in a wide variety of fruits, vegetables, whole grains, nuts, fish, low fat dairy products, and lean meat. Overall, the decrease in energy intake resulted in a decrease in body mass index (BMI) from 23.7 kg/m2 to a steady BMI of 19.5 kg/m2 and a reduction of total body fat percentage. The members' metabolic and physiological data reflect CR's powerful protective effect against obesity, type 2 diabetes, and inflammation—similar to the results of animal studies.3 Cholesterol values (including total and LDL), blood pressure, anti-inflammatory markers, fasting glucose, and fasting insulin were all significantly lower, while HDL was significantly higher in the CR group vs the Western diet group.3
In another study, participants experienced a forced reduction in calories, consuming between 1,750 and 2,100 kcal/day over an 18-month period due to a decrease in food availability. At the conclusion of the study, this group showed a marked reduction in blood glucose levels, lipids, and blood pressure.5
Additionally, Okinawans, known for longevity and low prevalence of age-related diseases, consume a nutrient-dense diet, often lower in calories than the average American diet. Their self-imposed habit of CR is referred to in Japan as hara hachi bu, which roughly translates to "eat until you are eight parts full (out of 10)." By leaving the meal without feeling 100% full, the stretch receptors in the stomach have time to notify the brain of satiation/fullness. In theory, Okinawans will eat 20% less simply by following this practice.7
All of these groups experienced health benefits associated with one form or another of CR.
Limitations of CR
Summary and Recommendations for Practitioners
Current data from epidemiological studies suggest that CR can exert beneficial effects on the factors involved in the pathogenesis of age-associated chronic disease and life expectancy.5 The research indicates that in healthy middle-aged participants, CR can result in reduced risks of life-threatening diseases such as cancer, diabetes, and heart disease. Consuming fewer calories can potentially improve overall health span (the years during which an individual is healthy and remains free from disease). It may also lead to increased longevity by the reduction of DNA damage and oxidative stress.11 Additional studies are needed to validate this, as human studies in this area are limited and of short duration.11,12 While research supports lower calorie consumption and a below-average body weight throughout life to reduce chronic disease and increase longevity, there are scant data supporting the beneficial effect of CR in elderly people.5 In fact, having energy reserves during times of stress, illness, and trauma can provide a protective effect and reduce mortality in this population.1 Multiple studies show that being overweight is related to better outcome in the elderly and excessive weight loss in elderly people is associated with poor clinical outcomes.1,5
Ultimately, practitioners do not have access to adequate information to make nutritional recommendations for patient intake and weight status in the latter decades of life. For motivated people in midlife, the health benefits of eating a nutrient-rich, calorie-reduced diet are well documented. However, the same cannot be said for their elderly counterparts. Therefore, additional research and policy development to establish healthy weights and nutrient requirements for older adults over the age of 70 are needed prior to making firm recommendations to this population. Assessment, education, and monitoring by a registered dietitian nutritionist with specialized knowledge in aging can be beneficial to decrease the risks of chronic disease and to promote longevity. Nonetheless, there is no evidence to support that complete CR is the only way to achieve beneficial results of reduced inflammatory markers and cardiometabolic risk factors,13 and it is worthwhile to note that CR is a commitment that relatively few individuals are consistently willing to make. Perhaps a more realistic approach is to encourage a small reduction in caloric intake and to avoid significant fluctuations in body weight through old age.
— Maureen Sykes, RD, LD, is a co-owner of S&S Nutrition Network, Inc, a Boise, Idaho nutrition consulting company specializing in geriatric nutrition. Her focus is on improving the lives of the elderly by providing optimal nutrition care through her consulting practice. Her areas of expertise include educating patients and caregivers on nutrition with a special focus on prevention of sarcopenia and malnutrition, and promotion of wound healing in the clinically compromised elderly population.
— Sue Stillman Linja, RD, LD, is a co-owner of S&S Nutrition Network, Inc. She has spent the past 25 years working with individuals in their later years, with individuals in pursuit of nutritional health and longevity, and those at life's end. She has recently authored the book, The Alzheimer's Prevention Food Guide: A Quick Nutritional Reference to Foods That Nourish and Protect the Brain.
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