Dietary intervention – or “biohacking” to reduce the societal impacts of Type 2 diabetes, obesity, and other metabolic disorders has been seriously studied in recent years, as these conditions continue to rise in an aging population – and even among the young – with highly negative consequences on health, longevity and aging.

Early studies in the 1930s first established that calorie restriction  was effective in extending the life expectancy of laboratory rats. Other studies that were subsequently conducted have confirmed the extension of life expectancy by way of sustained calorie reduction in a variety of mammalian species.

This success with laboratory animals in promoting greater health and ultimate longevity has inspired gerontologists to pursue research into the therapeutic possibilities of caloric restriction in human beings.

Proven Benefits of Calorie Restriction

Debate exists, of course, on whether sustained calorie restriction can actually impact the longevity of humans; however, there is a growing consensus that the practice of restricting caloric intake at any age can contribute to improved quality of life. It has been established, over the years, that some metabolic problems will respond to dietary modification, calorie restriction (CR) and other dietary controls, including such conditions as Type 2 diabetes and metabolic syndrome (symptoms of which include insulin resistance, central obesity, high blood sugar, high blood pressure, high serum triglycerides and low HDL, all of which are considered as contributing to a heightened risk of heart disease, diabetes and stroke).

“CR has been shown to beneficially affect glucose and insulin levels, preventing and even reversing conditions associated with hyperglycemia and insulin resistance. Given these observations, here is hope that targeted CRM may be identified or developed to favorably affect health span and life span through their action on glucose and insulin homeostasis” (Minor, Allard, Younts, Ward, Cabo, 2010). This positive effect extends to ameliorating or preventing such complications of diabetes, and of aging,  as stiffened joints, blocked arteries, and clouding of the lens of the eye that leads to cataracts.

Effects on Life Expectancy in Humans

The difficulty with gauging the effects of CR on extending the life expectancy of humans has been our current average longevity (for both men and women) of some 78 years, which would make it extremely difficult to maintain the strict clinical guidelines necessary throughout a longevity study of decades’ duration. In particular, it would be hard to find an adequate number of people willing and able to maintain a diet with a caloric intake of no more than 1,080-1,680 calories daily for such a long term, since  the paradigm for the current research into CR usually entails a reduction of from 20% to 40% of normal caloric intake. Maintaining such a highly restricted diet over a long term would be very demanding and, most likely, highly stressful for a great number of individuals.

Reduction of protein intake and intermittent fasting have been explored as ways to modify and adapt CR to modern lifestyles. While protein reduction shows some potential in extending life expectancy, based primarily on observations that populations pursuing a vegetarian diet appear to have a reduced risk for the many chronic diseases of aging, much evaluation remains to be done. Intermittent fasting, however, holds great promise, particularly since intermittent fasting (IF), as a dietary practice, has been shown to be both beneficial to health and sustainable over the long term. Fasting, in its various forms, has been in existence for centuries and is practice purely for health, as well as religious reasons, as a means of bodily purification or cleansing.  

Intermittent Fasting Study Results

Results of IF studies have been outstanding. “For example, overweight participants participating in a an 8-week study using IF (participants alternated daily between ad libitum intake [a diet that allows as much food as is desired] and 80%CR) lost weight and increased in measures of pulmonary function, perceived energy, and mood.” And, “Importantly, several recent short-term interventions have examined IF in non-obese humans and have found significant health benefits that parallel CR, including increased insulin sensitivity, upregulation of Sirt1 [SIRT1 is known as the Anti-Aging Gene, and is tied to the beneficial effects of CR], and decreased fat mass. Although the potential for IF to confer short-term health benefits to humans seems significant, IF’s effects on the aging process are not yet known.” (Minor, Allard, Younts, Ward, Cabo, 2010)

Calorie Reduction Study Results

The most recent CR study completed on humans – with results published in the March 2018 online physiology journal, Cell Metabolism(see – was conducted by the Pennington Biomedical Research Center in Baton Rouge, LA. Leanne Redman, the clinical physiologist who headed this study, found 53 healthy volunteers of normal weight to participate in the two-year study, who were willing to reduce their caloric intake by 25% per day.  A third of the volunteers (17 or 18 who participated) maintained their normal diet. The other two thirds remained on the severely reduced calorie diet for a full 24 months. Needless to say, this group lost an average of 25 pounds each, while the control group actually gained as much as 4lbs. each (Neighmond, Fulton, 2018).

The results? The metabolisms of those on the 25% CR diets slowed and became more energy efficient, meaning that their cells needed less oxygen to generate needed energy, and so fewer free radicals – the damaging byproducts of oxidation – were produced. The assumption is that reduced cell damage, resulting from production of fewer free radicals, should contribute to life extension.


However, Valter Longo,  a biochemist at the University of Southern California who studies longevity, cautions that severely restricting calories could mean that you would gain weight after a long period of CR, anyway, since – as you age – you would have to progressively reduce your caloric intake even more to maintain the same weight. Longo also expresses concern regarding the potential of a weakened immune system and considerable muscle loss after a severe reduction in calories over the long-term. He prefers a form of IF which he calls “mini-fasts.” These reduce caloric intake to 900 calories for just five days a month (presumably, once a week). Longo further proposes eating less meat, and more fruits and veggies (Neighmond, Fulton, 2018). The nutritional quality of the food you consume is very important, of course, and even more so on a calorie-restricted diet of any kind.

Severe calorie restriction should not be attempted by women of childbearing age who are pregnant or considering childbearing, and is contraindicated for a number of conditions. You should never attempt a major change in diet, and particularly severe calorie restriction, without first consulting your doctor.

Intermittent Fasting for Athletes – Fasting Styles and Effects on Performance

Another form of IF that works well for athletes is a single full-day fast per week, on a day when the athlete will neither train nor perform.

Yet another form of IF that is becoming popular and is easily adapted into most lifestyles, is a daily 16-hour fast followed by an 8-hour “eating window” during which food intake occurs, with the first meal being taken 6-8 hours after waking. Fluids are permissible at all times.

Current research involving athletes and intermittent fasting suggests actual enhancements in performance may be experienced when training during periods of little or no energy intake (a “low-energy state”), since this state aids in the production of a new mitochondria in a process known as mitochondrial biogenesis, which stimulates positive training adaptations to endurance exercisethat can enhance future performance (Pickering, 2019).

This mode of fasting is particularly attractive to some athletes, making it easy to maintain weight, and improving performance in such sports as weight training, where training during an early fast period leads to increased concentration that can translate into a performance with quicker reactions, fewer errors, smarter decisions, and –  in some athletes – more rapid gains in strength. Your fasting time should be coordinated with your training time, since some sports rely upon quickly burnable energy for high-intensity training exercises, like sprinting or resistance training. In these situations, it is important to consume sufficient nutrients and sources of immediate energy to train at an optimal level.

Muscle Protein Synthesis

Muscle protein synthesis is most efficient when the total daily intake is consumed every 3-4 hours, in portions of 20-40g. This consumption timetable “…provides a small advantage regarding muscle protein synthesis, which could affect muscle recovery and growth. And although the impact of this may be small, it could make all the difference for elite athletes” (Pickering, 2019). Depending on the volume of protein consumption, the 8-hour window may not allow enough time to easily consume the required amount.

So long as athletes monitor sleep quality and ensure their food intake provides a sufficient amount of calories and micronutrients, they should see no ill effects from whichever pattern of intermittent fasting best fits into their training and performance schedules.

Getting Started

To get you started on doing more research into adopting calorie restriction or an intermittent fasting diet, you may wish to consult the two Resources listed below the References.  

CR Society International is the online website of an international support organization for those individuals who are following, or are interested in following, a sustained Calorie Reduction (CR) diet. The website hosts online forums, posts photos of meals and recipe suggestions, and offers personal experiences, Society activities, blogs, and a variety of scientific and non-scientific articles on calorie reduction. The Society also hosts conferences. CR Society International website can be accessed online at

Peter Voss (Voss, 2009) is a calorie reduction aficionado who has compiled a helpful guide to maintaining optimum nutrition on a CR diet. His website is at 


Minor et al. (2010). Dietary Interventions to Extend Life Span and Health Span Based on Calorie Restriction. [online] Available at:   [Accessed 1 April 2019]

Neighmond, P. and Fulton A. (2018). You May Live Longer By Severely Restricting Calories, Scientists Say[HCT1] . [online]  Available at:   [Accessed 1 April 2019]

Pickering, C. (2019)  Intermittent Fasting For Athletes: What Does the Research Say? [online]  Available at:   [Accessed 1 April 2019]


CR Society International. (2019). [online] Available at:   [Accessed 1 April 2019]

Voss, P. (2009). CRON – Calorie Restriction with Optimal Nutrition. [online]

Available at:  [Accessed 2 April 2019]