Unintended caloric restriction in Biosphere 2
Caloric restriction reduces the risk of cardiovascular disease in several animal species. But what about humans? Data from the eight inhabitants of Biosphere 2 showed that people eating a low-calorie diet improved cardiovascular risk factors. In 1991, eight people (four men, four women) were sealed in Biosphere 2 near Tucson, AZ, and began a two-year experiment in ostensibly sustainable living. The oldest participant and project doctor, Roy Walford, published a research study of the bodily changes that the Biosperians exhibited during and after their stint in the Biosphere. The participants provided blood samples and underwent other tests to document changes in physiology and health.
As it happened, the Biosperians weren’t able to grow sufficient food to reach their target average daily caloric intake. For almost 90 percent of their stay, Biosperians consumed a low-calorie (1,750-2,100 per day), nutrient-dense diet from plants and animals they raised. The bill of fare consisted mostly of vegetables, fruits, nuts, grains, and legumes, with small amounts of dairy, eggs, and meat. By current standards, their diet would be considered healthy. Generally speaking, within a month after entering the Biosphere, participants’ body-mass index, systolic and diastolic blood pressure, blood sugar, total cholesterol, LDL-cholesterol, and triglycerides dropped substantially in a healthy direction. Participants exhibited excellent health, while sustaining high levels of physical and mental activity over their two years in the Biosphere.
Interestingly, shortly after exiting the Biosphere, all of the foregoing factors reverted to near their pre-Biosphere physiological levels. Photos show Walford looking emaciated (yet biologically healthy) at exit and highly fit-looking (but perhaps less fit physiologically) 18 months later after resuming ordinary living. This study suggests that long-term (two-year) caloric restriction can produce greatly improved physiological profiles and better overall health.
Physiological benefits of a healthy diet
Physiological and metabolic dysfunction appear to drive atherosclerosis risk. A study published by the National Academy of Sciences revealed the physiological benefits of humans eating a good quality, low-calorie diet. The study subjects included 18 members of the Caloric Restriction Optimal Nutrition Society in the US and Canada who lived for 3-15 years (average = 6) with severe (upwards of 50 percent), self-imposed caloric restriction. Sign me up! The 15 male and 3 female subjects ranged in age from 35 – 82 years (average = 50), all non-smokers and in good health. The 18 individuals were matched in terms of age and socioeconomic status with 18 control individuals who ate a typical American diet. Based on self-reports, members of the caloric restriction group appeared to eat a healthy diet characterized by vegetables, fruits, nuts, dairy products, egg whites, wheat and soy proteins, and meat, while avoiding trans fatty acids and high-glycemic foods (with lots of sugar and/or white flour).
Members of the caloric restriction group had marked lower average body-mass index than the control group: 19.1 versus 26.9. These numbers translate body weights of 136.7 and 192.3 pounds, respectively, a difference of 55.6 pounds for a 5’11” inch male. Those in the caloric restriction group also had markedly better risk factors for atherosclerosis than those in the control group. For example, HDL cholesterol: 63 versus 48; triglycerides: 48 versus 147, systolic blood pressure: 99 versus 129; fasting insulin: 1.4 versus 5.1; and C-reactive protein (a marker of inflammation): 0.3 versus 1.6. It’s impossible to determine if the greatly reduced risk of cardiovascular disease arose from severe caloric restriction, or a high-quality diet, or both, or other factors. But the impressive results warranted further study of healthy, low-cal diets.
Experimental evidence that caloric reduction lowers cardiovascular risk
Would a long-term randomized, controlled trial of caloric restriction—the gold standard in research studies—confirm the results of longitudinal results? CALERIE is a multi-centered, two-year trial in which 238 young and middle-aged, evidently healthy US adults (aged 21-50 years) were randomized to either a calorie restriction (CR) group (target of 25 percent calorie reduction) or a control group (asked to maintain their current dietary habits). After two years, participants in the CR group actually achieved an 11.9 percent calorie reduction, while the control group participants reduced their caloric intake by 0.8 percent. Thus, 25 percent caloric restriction might not be feasible over the long term for most people.
Phase 1 of the CALERIE study found that cardiovascular risk factors, including total cholesterol, triglycerides, LDL-cholesterol, systolic and diastolic blood pressure, and blood sugar all improved significantly for the CR group. It wasn’t clear if these cardiovascular risk factor improvements arose from caloric restriction or weight loss or some combination of the two. The study suggests that moderate caloric restriction is feasible, at least for two years, and improves cardiovascular risk factors.
More experimental evidence for caloric restriction benefits
Phase 2 of the CALERIE study evaluated the ability of caloric restriction to improve additional factors related to reduced hypertension, chronic inflammation, arterial damage, and oxidative stress, all of which are associated with better health and improved aging. Specific examples included body weight, body fat, C-reactive protein, and metabolic syndrome score, along with insulin sensitivity. Plus, researchers found that these benefits occurred independent of weight loss. These impressive results suggest that young and middle-aged adults who embrace a healthy, modestly calorie restricted diet can greatly reduce their risk of cardiometabolic disease. Ready to give a healthy, low-cal diet a try?