The knowledge that a lifestyle of reduced caloric intake results in greater health and longevity goes back to the 1930’s (1935 specifically) when Clive McCay and associates found that rats on a reduced calorie diet lived significantly longer than those fed ad libitum (1). In fact, the only variable outside of genetics (which we can’t control) that has any effect on the rate of ageing on a range of species seems to be caloric intake. It has consistently been shown in various species that restricting food intake to a level below that which would be consumed voluntarily results in a decrease in the rate of ageing and an increase in the average and maximal lifespan (2, 3). Calorie Restriction (CR) has even been shown to reduce cancer formation (4, 5), kidney disease (6), and increases the resistance of neurons to dysfunction and degradation in experimental models of Alzheimer’s disease and Parkinson’s as well as stroke (7-10).
The science community defines ageing as the biological changes that occur over time that result in a reduced resistance to stress, increased vulnerability to disease and increased probability of death. In addition to decreasing the ageing process and increasing longevity, CR has also been shown to have several health benefits including increased insulin sensitivity, stress resilience and reduced morbidity, and scientists at Washington University in St. Louis published research showing that people on calorie-restricted diets had hearts that function more like those found in people two decades younger.
But further research is still being tested to this day as to the exact reasons or mechanisms by which (CR) works. Scientists speculate the benefits may be linked to an adaptive response. As in, when food is too sparse an animal can’t reproduce, so its aging process slows down to buy time until food becomes plentiful again.
Calorie restriction typically refers to a diet which limits caloric intake relative to one that allows feeding to be completely free and unrestricted. This free Ad Libitum (AL) consumption has been compared to different schemes of CR such as Limited Daily Feeding (LDF) which typically involves 10-40% restriction from usual AL amounts, or Intermitted (alternate day) Fasting (IF) which allows free feeding one day followed by complete fasting the next in constant alternation.
Interestingly, while many of these studies show that LDF results in lower body weight (as expected) and increased life span supposedly due to its restriction in calories, the findings from IF regimes have shown that the IF animals consume almost the same amount of calories over the 48 hour period as the AL groups, signifying that they consume almost twice as much on feeding days after their fast day, with less significant body weight changes and yet, they still produced the beneficial results in longevity and health parameters. In fact, IF resulted in beneficial effects that ‘met or exceeded’ CR including reduced blood glucose and insulin, and increased resistance of neurons in the brain to excitotic stress. This may suggest that it is not simply the calorie restriction alone as much as it is the periods of fasting that produce the advantageous adaptations, or else the IF groups would have not seen improvements since their caloric intakes over time were similar to the AL groups.
An important point to note is the addition of what they call Calorie Restriction with Optimum Nutrition (CRON) to the ongoing research into CR over the years. Since CR alone typically leads to a lower nutrient intake (due to the lower food intake) the CRON diet takes this into account and provides under-nutrition (calorically) without mal-nutrition (nutrient-deficiency). Originally, when studying the effects of retarded body growth on length of life, the early studies restricted both calories and nutrients and found that malnutrition caused metabolic problems, tumours, and even pre-mature death. It was only when they added the nutrients for CRON that it worked well in rats. Then in 1937 there was a similar study of water fleas that showed that reduction in food given to juvenile water fleas delayed the start of reproduction, extended the reproductive period and extended lifespan.
While we haven’t had conclusive studies on humans (it’s hard to do life-long studies in humans involving complete lifestyle control and CR, for some reason people just don’t volunteer very often), preliminary observations of physiological changes caused by CR indicate that life-extending effects will probably be observable in humans as well. While a study by the NIA (11) actually found contradictory results in Rhesus monkeys, our close relatives, showing CR did not improve the average life span in these longer lived primates, it did find correlations with beneficial health predictors and positive results in many age-related diseases. And further research has found parameters such as BMI, cardiovascular risk, cholesterol, blood pressure, fasting glucose and insulin levels, and body fat percentage, have all shown positive results in short-term CR in humans (12-13).
So the question then becomes “does varying the amount of calorie restriction have differential effects on lifespan and age-related diseases. It was answered in part in 1986 by Weindruch and co (14) who showed the maximum lifespan increased with increasing amounts of calorie restriction in rodents and then only up to a certain degree (above which it becomes detrimental due to death by starvation) but later investigations showed in non-human primates modest levels of CR can significantly reduce age related disorders because such low levels of CR as in rodent models would unlikely maintain life in higher primates. The more complex the species; the more modest CR seems to be favorable.
Modern Habits
Many of our prevalent diseases of today (CVD, Diabetes, obesity, hypercholesterolemia), are a result of dietary choices. Basically our modern day diet is one built on habitual excess/gluttony because we have a constant supply of calories and endless variety of processed foods. When we have a continual supply of empty calories basically on tap drip-feeding into our arteries without so much as a breath of cessation there’s little wonder why obesity and lifestyle diseases are so prevalent. Some might say we have even become dependent on it. We have been so entrenched in this lifestyle that people fear going without food for ‘health reasons’, despite this very reason being the cause of the vast majority of our health problems.
Put simply, to live as our distant relatives once did when they were not so fortunate as to have food at hand served up on a silver platter 24/7, when they often went without a meal or much food for periods at a time, this is the lifestyle that has been linked to adaptive responses which lead to greater resilience in health. Hunter gatherers would hunt for food, sometimes all day long, often unsuccessfully. The stone-age was feast or famine, make a kill and devour it or go without until next time. Not three square meals a day and certainly not six meals a day.
I hear you thinking – they grazed right? That’s eating small amounts throughout the day. Yes, but foraging barely constitutes a meal. I’m not saying six meals a day is not good – I like it, and still eat sometimes as many as eight times day, but there’s a difference between short-term anabolic periods (muscle gain being the typical goal) and living sustainably for most of the time on a balanced, conservative diet.
For most people, when trying to manage weight and sustain a healthy system, calories should be low (low density foods) and blood glucose should be left to drop at times and even for many hours at a time. The only ways to do this is by eating low calorie-dense foods or simply fasting for periods. This is the exact opposite of constantly drip-feeding calories into your arteries. Unless you’re a super athlete expending enormous amounts of energy daily in training or competition akin to the elite, you can’t have high blood sugar constantly for years on end and live to tell the tale.
This does not mean long periods of time without food or prolonged starvation is idealistic for anyone, especially those who want to slap on a bit of muscle mass here and there. Although, it also doesn’t mean this would be detrimental (according to the health research), it just tells us why we definitely do want to avoid excess consumption of unnecessary calories, and why every now and then going without (or with little) for a while is beneficial. The original research into the topic of CR and longevity started because of the link between body size and life span (less calories in rats resulted in stunted growth which correlated with longer life). So we know that too few calories will inhibit maximum potential on growth – completely detrimental to the muscle-gain devotees. Yet, there is still much benefit in a controlled caloric intake with respect to both physique and health/longevity.
Ultimately, it seems many benefits can come from modest CR and from brief periods of fasting or low blood glucose, provided we still maintain adequate nutrition from a nutrients perspective. It goes without saying that if you currently overeat significantly compared to your activity level then reducing calories is a no-brainer, but since the studies in humans thus far have not progressed enough to include specific populations such as diabetics, seniors, children, etc., it is always wise to consult a professional if you consider implementing any form of significant CR into your own life.
1. McCay CM, Crowell MF, Maynard LA. The effect of retarded growth upon the length of life span and upon the ultimate body size. J Nutr. 1935;10:63–79.
2. Masoro E J(2000) Exp Gerontol 35:299–305.
3. Weindruch R, Sohal R S(1997) N Engl J Med 337:986–994
4. Blackwell B N, Bucci T J, Hart R W, Turturro A(1995) Toxicol Pathol 23:570–582.
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6. Fernandes G, Yunis E J, Miranda M, Smith J, Good R A(1978) Proc Natl Acad Sci USA 75:2888–2892
7. Bruce-Keller A J, Umberger G, McFall R, Mattson M P(1999) Ann Neurol 45:8–15.
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11. Impact of caloric restriction on health and survival in rhesus monkeys from the NIA study. 2012 Sep 13;489(7415):318-21. doi: 10.1038/nature11432.
12. Elisa Zied, Some Try Calorie Restriction For Long Life, MSNBC, Oct 5, 2007
13. Fontana, L. (2004). “Long-term calorie restriction is highly effective in reducing the risk for atherosclerosis in humans”. Proceedings of the National Academy of Sciences 101 (17): 6659–63. Bibcode:2004PNAS..101.6659F. doi:10.1073/pnas.0308291101.
14. Weindruch R, Walford RL, Fligiel S, Guthrie D. The retardation of aging in mice by dietary restriction: longevity, cancer, immunity and lifetime energy intake. J Nutr. 1986;116:641–54
