As a student in life sciences, many times I find myself excitedly relating a subject to an Islamic teaching during our classes. That’s what happened when a professor was talking about cancer metabolism as she brought up the subject of calorie restriction. Basically, calorie restriction (CR) refers to a dietary practice of reducing the amount/variety of daily food intake in a controlled manner. The roots of this practice reach back to 1917, when a group of scientists claimed that restricting the food intake of four female rats extended their lifespan significantly (1). Since then, studies have followed in order to explore the effects of this practice in terms of aging, obesity, cardiovascular diseases, diabetes and finally cancer. In this rather summarized essay, I will touch on its studied effects in lifespan longevity and reduced cancer progression supported by scientific articles.

Although differences in practice exist in scientific experiments, we can sum up the calorie restriction method before going into the experimental evidence part. First, animals are observed and their daily calorie intake is calculated. The restricted animals are given some percentage of the food control animals consumed the preceding day. Although it can vary, this percentage is most often 60%-70%. All animals used are from the same sex and age and the parameters except calorie intake are kept constant as much as possible. Malnutrition was ignored by some early studies, but since it would affect the significance of the results, many scientists then opted for supplementing the restricted diet with vitamins and minerals or designed a restricted diet that would not potentially cause malnutrition.

One reason CR has been the focus of significant attention is that it is currently the only nongenetic method shown to increase lifespan across many species including yeast, worms, flies, rodents and primates. The most famous and breakthrough rodent study was from 1935 which was supported by the same scientists from three additional experiments conducted between 1939 and 1942. In this study, restricted calorie intake without malnutrition retarded growth in the rats and increased their lifespan. The study also claimed that the driving force of life longevity was the reduced energy consumption and not the lack of specific nutrients (2, 3, and 4). After the experimental protocols became more standardized with determined food variety and known percentages of each food type, new experiments still confirmed initial findings. In 2002, a group of scientists showed that aging rodents on CR showed more capability of physiological activities similar to younger rodents (5). Also, there are many studies in rodents showing that CR slows down or delays most age associated diseases. Moreover, even from the initial studies, some scientists found that CR practicing rodents had less spontaneous tumor occurrences and avoidance of obesity either delayed or prevented cancer occurrence (6, 7).

The results are not as direct in primates and humans, as expected. Indeed, there are relatively fewer studies in primates most prominent of which was performed on rhesus monkeys. One of these studies, performed throughout 20 years on 46 female and 30 male monkeys proved that CR almost diminished cancer occurrence and decreased age related deaths while also increasing physical activity ability in aging monkeys (8).

In relation to us humans, the application of CR changes . Some scientists claim that instead of the regular CR method, intermittent fasting would be more adjustable to the human diet supported by studies that show this kind of fasting (every other day feeding) in mice led to CR associated benefits. Nonetheless, there is one big group (CALERIE) who studied CR from 2007 to 2012 among 218 volunteered non-obese healthy young humans. Adjusting regular application to the human diet, researchers used 25% reduction in daily calorie intake after proving it was safe for the subjects. The results are continuously coming up from this study, but so far it seems that the CR practicing group had improved overall health, improved mood, reduced tension, improved sleep duration, improved blood sugar levels and better reproductive health besides an obvious weight loss (9). For those interested, here is a story in NY Times including interviews with volunteers in this study.

The possible life extending effects of CR has yet to be proved valid in humans, and scientists say that CR is not for us to implement into our lives as it is. They say it is to study aging and the mechanisms involved. Most of the current literature on CR talks about its potential effects and yet, still so little is known about the pathways and systems that cause these effects. There are interesting hypotheses including activation of our biological clocks as an example (10) or some genes that are thought to be activated with CR (11). The picture is still incomplete, but the take home message is clear: less is more, literally.

To be clear, I don’t need science to confirm if an Islamic teaching is beneficial. Rather, it truly amazes me to see how the human brain tries to solve the great design of our bodies and our world and the harmony between the two. The hadith I associated with this topic from the moment I learned about it is below:

Hadrat Abu Karima Miqdad ibn Ma’dikarib (may Allah be pleased with him) relates that he heard the Holy Prophet Muhammad (may Allah’s blessings and peace be upon him) say:

No man fills a pot worse than his stomach. For any person, a few mouthfuls are sufficient to keep his back straight. But if he wants to fill his stomach, then he should divide his stomach into three parts and should fill one third part of the belly with food, another third with drink and leave one third empty for easy breathing.


Moreover, I am sure many of you remembered Prophet Dawood (pbuh) `s fasting when you were reading about every other day feeding. As Muslims we believe that prophet Noah lived for centuries, and even old companions of our Prophet (pbuh) went to fight in wars in the name of Allah. Age was not a limiting factor in the times of our prophets (pbut).

The handbook of how to efficiently use our bodies is given to us in the form of Islamic practice. As the beautiful time of Ramadan Kareem is upon us, let us remember that handbook. May Allah guide us and help us utilize our health for good deeds in the name of Him. Ameen.

Fatma Betül Aksoy Yaşar


1. Osborne, T.B., Mendel, L.B., Ferry, E.L., 1917. The effect of retardation of growth upon the breeding period and duration of life in rats. Science 45, 294–295.
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3. McCay CM, Maynard LA, Sperling G, Barns LL. Retarded growth, life span, ultimate body size and age changes in the albino rat after feeding diets restricted in calories. J Nutr. 1939;18:1–13.
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Impact of caloric restriction on health and survival in rhesus monkeys from the NIA study.
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Effect of Calorie Restriction on Mood, Quality of Life, Sleep, and Sexual Function in Healthy Nonobese Adults: The CALERIE 2 Randomized Clinical Trial. Comprehensive Assessment of Long-term Effects of Reducing Intake of Energy (CALERIE) Phase 2 Study Group.
JAMA Intern Med. 2016 May 2. doi: 10.1001/jamainternmed.2016.1189.
10. Patel SA, Velingkaar N, Makwana K, Chaudhari A, Kondratov R.
Calorie restriction regulates circadian clock gene expression through BMAL1 dependent and independent mechanisms.
Sci Rep. 2016 May 12;6:25970. doi: 10.1038/srep25970.
11. Derous D, Mitchell SE, Green CL, Chen L, Han JD, Wang Y, Promislow DE, Lusseau D, Speakman JR, Douglas A.
The effects of graded levels of calorie restriction: VI. Impact of short-term graded calorie restriction on transcriptomic responses of the hypothalamic hunger and circadian signaling pathways.
Aging (Albany NY). 2016 Apr;8(4):642-63. doi: 10.18632/aging.100895.