Calorie Restriction Explained
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Calorie restriction (usually abbreviated to CR) is a strategy proven to extend healthy and maximum life span in rodents and primates. Some animal studies conducted over the past 20 years have shown up to a 40% increase in maximum life span - though there is good reason to believe that any gain in human life span through life-long CR would be much more modest.

Calorie restriction also provides numerous secondary benefits, such as a greatly lowered risk for most degenerative conditions of aging, and improved measures of general health. In recent years, human studies have demonstrated that these same secondary health benefits are available to you and I, not just to laboratory animals. Many researchers believe that the evidence to date shows the practice of CR will extend the healthy human life span, but a consensus has not yet been reached on this topic.

Calorie Restriction in a Nutshell

A calorie restriction diet aims to reduce your intake of calories to a level 20-40% lower than is typical, while still obtaining all the necessary nutrients and vitamins. CR is also known as CRON, for "calorie restriction with optimal nutrition," and its practitioners have accumulated many years of experience and experimentation. As a result, good books and a supportive community exist to help newcomers adopt the best practices for CR in humans. Mild CR may be as easy as adopting a much healthier diet, taking a few supplements and not eating snacks.

The degree to which CR can extend the healthy human life span is open to debate - and is the subject of vigorous discussion within the scientific community - but the evidence for at least some healthy life extension is compelling. A sampler of articles from the past few years illustrates this point:

  • Impressive Calorie Restriction Statistics
  • The Evidence For Calorie Restriction
  • CR Reduces DNA Damage
  • CR Beneficial Late in Life
  • Calorie Restriction Cleans Cells
  • CR Enhances DNA Repair
  • Study Backs Human Calorie Restriction
  • CR Protects Against Heart Aging
  • CR Slows Immune System Aging
  • CR Slows Alzheimer's Progression
  • CR Reduces Stem Cell Decline
  • CR Reduces Inflammation and Muscle Loss
  • Before going further, it is a good idea to read the Fight Aging! disclaimer and take a few moments to think about responsibility and health. It is a wise idea to consult with your physician before embarking on any change in diet aimed at improving your health or longevity, especially if you have a medical condition. There is no substitute for taking personal responsibility in health and research!

    That said, on with the discussion of calorie restriction. You may have seen CR mentioned more often and in more detail in the mainstream media of late; the phrase "low-calorie diet" has also seen a lot of usage. To be precise about these terms, calorie restriction is simply the most widespread and well-researched form of low-calorie diet.

    Modern CR Science

    The beneficial effects of CR in laboratory animals have been known for a long time, but only in the past decade - and in particular over the past few years - has more funding and effort been devoted to this field. In the present day, human studies such as CALERIE are underway and many research groups are digging into the biochemistry that could explain how and why CR is so good for health and longevity.

    The genes and processes that control metabolism are notoriously complex, and scientists do not yet have a complete understanding of the way in which CR fits into the overall picture. But they are working on it.

    Many reputable health websites maintain an informative section on CR. Unfortunately, some of these resources exaggerate minor difficulties experienced by people who practice CR - this is something you will see in the media as well. An article from MSNBC in early 2003 went so far as to use the word "torturous" to describe the experience of trying CR! This is all far from true: starting on CR is no harder than any other diet change.

    Weight loss should be mentioned in the context of CR, even though it is not the primary goal of a CR diet - if you eat fewer calories, you will slim down. Research indicates that being overweight, or carrying excess body fat, is harmful to your long term health in many different ways. Excess weight increases risk factors for conditions ranging from diabetes to cancer to Alzheimer's, most likely due to the relationship between fat cells and chronic inflammation. It is no exaggeration to say that if you are overweight, you will have a shorter, less healthy life - many recent studies suggest that even comparatively little excess weight is bad for you over the long term, significantly raising your chances of suffering a range of age-related conditions. Some portion of the health benefits of CR are likely to stem from the accompanying loss of weight and body fat - although biochemical research indicates that there is clearly more than just that going on under the hood. CR is also doing something positive with the controlling mechanisms of metabolism.

    For example, it appears that CR provides a boost to the process of autophagy. Autophagy is the way in which your cells remove damaged components in order to recycle the materials into new replacement parts. Several lines of research indicate specific types of damaged cellular components left to cause problems over time contribute to age-related decline and damage inflicted upon the rest of your body's machinery. More autophagy may help reduce this contribution to the aging process.

    How to get started on CR? You'll find a wealth of information and many, many starting points out there, some of which can be quite intimidating to the newcomer. You might find the following path useful:

    Obtain a Copy of "The Longevity Diet: Discover Calorie Restriction"

    This book is a very good, easy introduction to the principles and simple ideas behind calorie restriction. Beyond that, it is a practical guide that will help you over a lot of the early pitfalls. It handily answers the "what exactly is it I eat?" question and offers some great tips for new practitioners.

    Practice Eating a Better Diet First

    While you're waiting for your book to arrive, you can start to shift your diet in preparation. Have a look at this resource for a class of diets known as "Paleodiets":

    The selling point of Paleodiets is that they replicate the hunter/gatherer diet of our ancestors, and are therefore better for us. This is not an argument advocated here at all, but Paleodiets make a great introduction into calorie restriction.

    One thing you'll find out quite early on in your journey into calorie restriction is that you'll have to stop eating a lot of highly processed, rich, modern foods. They are heavy in calories and light in nutritional value. In the US, you can walk into any corner store and eat 1500 Kcal of junk food (chips, chocolate, and so forth) at a cost of $10. You'll be hungry again a few hours later. That same $10 could feed you for two days if you buy vegetables, rice and tofu. You could eat 1500 Kcal a day and hardly be hungry at all.

    These two examples are at the opposite ends of the spectrum, but most people eat far more rich food and many more "empty calories" (calories that do not provide vitamins and essential micronutrients) than they should. Adopting a Paleodiet for a while is an easy way to start thinking seriously about what you eat, how you cook, and how you can better organize your eating habits. It's a smaller and more manageable jump than leaping straight into calorie restriction.

    If you were eating an unhealthy diet before trying this, you'll probably notice the benefits of healthy eating within a few weeks. Your palate will become more sensitive to subtle tastes, you'll need less sleep, feel more alert, and mood swings will be diminished. Much of this stems from cutting processed sugars.

    Pay Attention to Calories

    Counting calories is a good thing, and it's something that you have to pay attention to. Your body will let you eat far more than is good for you, so your brain is going to have to take over managing the process.

    Almost everything you buy from the grocery or supermarket has the calorie content listed on the packet. Note that most manufacturers list calorie content by portion, and that even a lowly bar of chocolate usually has two portions. Marketing departments don't like the number of calories to be too high, as people won't buy it...so they'll just divide the product into more portions with a lower calorie count per portion. Sneaky!

    Most foods have more calories than you might think. You can recognize the new practitioners of calorie restriction at the supermarket: they'll be the ones looking at many different product packages and muttering "wow, I had no idea!"

    For foods like apples, rice, loose vegetables and so forth, you will need a book of calorie values. Recent editions tend to contain (fairly horrifying) values for fast foods as well as the more usual suspects. You might try the well regarded "Food Values of Portions Commonly Used":

    If you'd prefer an online reference, NutritionData provides a wealth of searchable information on various foods:

    Remember the Supplements

    You should always take a good multivitamin supplement (at the very least) when on a calorie restriction diet. In theory, it's perfectly possible to obtain all the vitamins and micronutrients you need from your food. In practice, for most people living busy, working lives, this just isn't going to happen. Remember to take your supplements.

    The Water Trick

    Doctors tell us that few people in Western societies drink as much water as they should for optimal health, and many people mistake low-level thirst for low-level hunger. A very helpful tactic for those practicing calorie restriction is to drink a glass of water when first feeling hungry. If you are still hungry twenty minutes later, then maybe it's time to think about eating. Half the time, you were just thirsty, however.

    If You Have Questions, Ask!

    There is a large and very helpful calorie restriction community out there.

    Visit the CR blogs, take a look around, join the CR Society mailing lists and feel free to speak out. These folks have plenty of advice and helpful hints for newcomers. Everyone was new to calorie restriction at some point in the past, and there are no stupid questions.

    It's Just a Diet, So Relax

    Too many people approach diets in an all-or-nothing way. If they slip up or eat poorly one day, they become stressed or abandon the diet entirely in frustration. The key to health through diet is a relaxed attitude. If you slip up, let it go. Keep at it, do better next time, and stay working on the average.

    Remember that a diet is simply a tool to make you healthier, and thus enable you to keep up with what you enjoy in life. Good luck in trying CR!

    Addendum: The Future of Your Longevity

    If you've read this far, you are probably interested in living a longer, healthier life. Calorie restriction is still the only widely available tool in the longevity toolkit today, which, when you stop to think about it, is a rather sorry state of affairs. This will not always be the case, however, as medical science and biotechnology are advancing ever onwards. It is worth remembering that, as time progresses, your remaining healthy life span is determined ever more by the rate of progress in longevity research - work aimed at repairing the accumulation of cellular damage, the roots of all age-related disease and infirmity.

    You should look into calorie restriction today, but also consider the long-term view: supporting medical research into extending healthy longevity is just as important ... and it will become ever more important as time goes on that you made that effort to help the development of better longevity medicine.

    Last updated: December 7th, 2010.

    Comments

    Very interesting. I did not know about this.

    Posted by: Andualem Anteneh at January 3, 2011 11:33 PM

    looks a little daunting for a first timer, but will give it my best effort..

    Posted by: David at January 17, 2011 1:30 PM

    I am curious as to your thoughts on the idea of "negative calorie" foods, if they might apply to CR and if there might be a way to prove or disprove it. I've done searches and bought an ebook but have found no proof for or against the idea. Seems to me there should be some foods that require more calories to digest than they can supply to the body.

    Posted by: dale at January 26, 2011 5:25 PM

    @dale: the triggers for the benefits of CR apparently involve, amongst other things, sensing food, levels of amino acids in the diet, and to some degree the level of fat tissue in the body. Flies can gain most of the benefits of a CR diet through a low methionine diet at normal calorie levels, for example.

    Negative calorie foods may or may not exist, and you're certainly going to have trouble finding reputable information out there.

    But CR is about absolute calorie intake, not net calories in minus calories burned. Athletes on high calorie diets may be pretty healthy because they're exercising to burn it all off, but they're not practicing CR nor are they in any way gaining the benefits of CR.

    Posted by: Reason at January 26, 2011 5:39 PM

    I've found intermitent fasting (IF) to be the easiest and quiet enjoyable. I fast three days a week--- Monday, Tuesday and Thursday.... I've done this for a year and half and actually look forward to fast days. on the days I do eat, it's sensible without restrictions (my stomach shrinks from the days of fasting, so you really can't eat crazy. I love my IF diet!

    Posted by: mory at May 8, 2011 8:02 PM

    I have know about CR for a very long time, but only recently decided to take it on as a lifestyle. It's only been about 2 weeks, but I'm loving it already.

    Posted by: cron living at June 22, 2011 9:05 PM

    Hello from Australia. I am a 50 year old male who has been on a CR diet for the past 20 years. I sort of fell into it without initially realizing the health benefits. At age 30 I carried out a 50 day liquids-only hunger strike to protest rainforest destruction. My appetite never returned, and a doctor told me at the time that we have two appetites - a time dependent appetite and a smell dependent appetite. He said I had lost my time-dependent appetite, which is like a 'habit-based' appetite. For example at lunch time your body tells you that you are hungry as it is in the habit of being fed at that time - not because you have a sudden need for an infusion of nutrients. Anyway, I digress. Back to the CR diet. I generally eat one small vegetarian meal in the early evening, although if I really feel like meat I will eat a small amount. I usually just have coffee for breakfast and lunch, which keeps me regular, protects me against lower bowel cancer, and is a liver tonic. At 50 I weigh the same as in High School (around 67kg), have slightly low blood pressure, perfect cholesterol levels, and no signs of mid-life age related diseases. My older brother at 52 has eaten a normal western diet all his life and is 'slightly obese', pre-diabetic, and has high cholesterol and high blood pressure. As we are very close genetically I believe these differences in our health indicators are totally due to diet.

    Posted by: Brett Pritchard at July 5, 2011 12:08 AM

    I've been very interested in CR myself, but I think this article fails to even list the potential downsides well enough. I've put together a little article myself with many references to scientific articles, in case anyone wanted to look into it further.

    http://www.brainlings.com/2011/11/caloric-restriction-analysis/

    Posted by: mrnuts at November 5, 2011 3:54 AM

    The whole idea of CR makes perfect sense really. The less we eat, the less the body has to work to expel all the waste products and the more efficient the body becomes at utilizing the energy that is consumed. The more a car is driven, the faster it will break down, especially if it runs on dirty fuel! I am keen to try this diet. Just have to get rid of my sweet tooth.

    Posted by: Simon at December 27, 2011 3:39 AM

    That sweet tooth has a lot to answer for, doesn't IT?

    Posted by: Michael at December 29, 2011 11:40 PM

    I have a question about CR, it would nice if one of the moderators here could address it whenever possible. I'm wondering if CR can be regarded as the same as having a low percentage of body fat. Because I don't restrict my diet at all, but through exercise and healthy eating I have a low BMI. I have some of the same side-effects of CR, such as cold sensitivity and low blood pressure, and I would (obviously) love to have some of the benefits as well. Many athletes have excessively low BMIs, much lower than mine, and don't restrict their caloric intake at all. In fact, in order to maintain great strength and muscle mass, they're forced to eat more. So what exactly is it: low intake or low fat?

    Posted by: Amy at January 8, 2012 8:12 PM

    To the comment moderator: nevermind. I've read through the website a little more and have found the answer to my previous question. From what I understand, lower body fat aids in a healthier immune system, but that's not the whole picture.

    Posted by: Amy at January 8, 2012 8:15 PM

    @Amy: Short answer: it's intake, but lower levels of visceral fat have their own benefits.

    The benefits of calorie restriction are likely a combination of effects, of which lower levels of visceral fat is but one (and probably a minor one). Visceral fat is certainly bad for you in excess:

    https://www.fightaging.org/archives/2008/03/lose-the-visceral-fat.php

    Exercise improves healthy longevity through a separate collection of mechanisms, with a small amount of overlap with calorie restriction - such as the lower levels of fat, and increased autophagy.

    The trigger for metabolic and other biochemical changes brought on by calorie restriction is largely reduced intake of dietary protein methionine:

    https://www.fightaging.org/archives/2010/01/methionine-restriction-as-the-cause-of-calorie-restriction-benefits.php

    Posted by: Reason at January 8, 2012 8:21 PM

    I have an over active gallbladder. The doctors wanted to remove it but I told them I would try to control my symptoms with diet. Tried several diet strategies and the one that works is eating one meal a day. It turns out I backed into CR in the process. That lead me to this web site. It works for me. I’ve never felt better.

    Posted by: Edward at March 3, 2012 4:13 PM

    This is a good introduction to CR. I am pre-diabetic owing to long term chemo as a child. I'm doing the CSIRO total wellbeing diet at the moment, which is brilliant, as it is nutritionally balanced, and am able to cut calories significantly without feeling hungry and getting too many sugar swings. I suppose this is a watered-down version of CR. Feeling so much better by eating less.

    Posted by: Teresa Steele at March 15, 2012 6:38 AM

    Well, I had heard of calorie restriction before and always thought that it was not for me. I would love to extend my life but not enough to cut out good eating; I am a bit of a gourmand. Anyway, I recently discovered that I had become lactose intolerant and shortly afterwards stopped being able to digest wheat. I don't think it is anything to worry about because these two complaints are things that my mother and brother have been complaining of for years so I suppose it was just a matter of time.

    I now discover that I can almost eat nothing and am largely living on oat clusters and berries with lactofree in the morning and sushi for lunch with a possible wheat free sandwich at night. Since I stopped eating wheat I have found that I no longer get food cravings. I used to just stuff myself but I guess I must be better able to absorb my nutrition without the wheat in my diet.

    The thing that brought me to this site was a websearch because I had noticed that I was regularly sleeping for less then seven or six hours a night now. I had forgotten about CR so I was pleasantly surprised to discover I could expect extended lifespan as well. I do not go in for the constant calorie counting but I reckon as I lost 5 pounds in the last 10 days I must be on a CR diet. I have always paid attention to nutrition so although I probably could make an effort to eat a little more healthily I am certainly not eating rubbish.

    It is odd that what I had once considered as too difficult and unpleasant to even try I have had imposed on me by nature and is actually not even all that tricky in practice.

    Posted by: Ro Atkinson at April 19, 2012 6:10 AM

    I'm 81.I have always kept slim,weighing 10st 4lb as I did at eighteen. I reduced my 18-1900 cals/day to 1200 without problems a year ago. Not hungry or cold. Intensive Interval training regime. Weight still 10.4 surprisingly. Aim not to live for ever but to die suddenly,unexpectedly,and in the best of health!
    BP av 112/68 resting pulse 9bpm. fasting blood sugar 86.Total cholesterol

    I reckon CR is easy and very beneficial. I certainly feel fine on it, and slight arthritic rwinges have disappeared.

    Posted by: simon at April 27, 2012 11:11 AM

    I do think there is something to the CR diet - I have also fasted in my life and I know the benefits of healing that can be accomplished when you let your digestive system rest. Animals fast quite naturally when they are not sick. Humans should do the same - it's in the Bible as well to fast. Doctor supervised, fasting clinics can be found in Europe but books on fasting are very fascinating to read and the few times I have put myself on a long fast, I could tell that there was a healing process of the mind, body and soul. Good luck with your endeavours - you are on the right track.

    Posted by: Dana Montez at May 14, 2012 8:26 AM

    I am a 62 year old male who just started a CR diet. My eating habits have steadily improved over the years as I have become more sensitive to foods that are bad for my health. But before CR, I was only able to maintain my weight, not lose weight. I have been on the CR diet for 6 weeks and have lost 6 pounds. I eat a healthy breakfast and lunch, but try to limit dinner to a healthy snack such as fruit or some vegetables. I am not too concerned about getting enough nutrition as I have been a supplement fanatic for several years. I am never sick. My activity level varies from day to day. My biggest problem is that I get hungry easily. I want to reduce my body fat and get down to a weight I can maintain. I am at 20% body fat. What is a safe range for body fat? I am hoping that once I reach my weight goal, the hunger will be easily managed.

    Posted by: Michael Kelly at July 29, 2012 8:20 AM

    we are using calorie restruction,it works good for me,however my wife says it makes her tired she has quit carbohobrates,can you advise us why and what to do?

    Posted by: richard hughes at August 6, 2012 11:52 AM

    I am planning to start CR but am obese at the moment (30% fat) i have a fascination with data and would like to participate in or start an experiment that would be useful to others. Does anyone know of individuals or groups running or supporting CR experiments that we can join or be guided by?

    Posted by: Jolyon at September 3, 2012 1:06 AM

    Does anyone know go any good sites that have recent articles on CR? any recent studies or evidence out there that i can read. I think the CR diet is the most logical and i have started to follow it, I am just sick of trying to defend myself to people that think i am an idiot for "not eating enough" or "you need to have some bad food" etc etc I'm sure you have all heard it before, having something to defend myself with would be good!

    Posted by: Chloe at November 13, 2012 10:55 PM

    I have tried calorie restricting diets to lose weight, but I was far too hungry to carry on with them, then I saw a programe on television about alternate fasting. I tried it, but couldn't cope with restricting myself to only 500 calories as I'm a piggy and like my food too much.

    I decided to restrict my calorie intake for two days a week to 1,000 calories on Mondays and Thursdays as I couldn't handle two consecutive days with food restrictions. It worked. I have lost three pounds already in less than two weeks and have only half a pound more to lose. I hope that once gaining my target weight I need only restrict my calories for one day a week.

    My memory has improved and I have more energy than before. The strange thing is that on the days after eating only 1,000 calories I had four meals and I was still losing weight. It's as if my body went into burn up mode. I intend to stick with it as it's successful and means I can eat normally for five days.

    Posted by: Angel at January 19, 2013 3:22 PM

    Hasn't research now revealed that calorie restriction doesn't extend lifespan in primates?

    Posted by: Libby at September 11, 2013 10:59 PM

    I have been hearing and reading about CR for some time.Some of the initial research has been debunked; however like most eating plans, it has some merit. I see no reason to take it to extremes however.
    As far as I can see, one of the most important things is to eat enough roughage so that you poo really regularly. I have seen bowel cancer in relatives and it isn't pretty. I believe some CR believers eat vast quantities of vegetables and fruit, which makes sense.
    On the subject of supplements - personally I can't afford them, they are really expensive, so I do try to get as much nourishment from my diet as I can.
    I do know one person who fasts regularly and does CR,but does no exercise at all. Yes he is thin, but no muscle tone to speak of. I think you need to work out at least moderately for optimum health.

    Posted by: Ros at November 12, 2013 11:08 PM

    I think CR is extreme, & a club for those who want to be bone thin & willing to work at getting the correct balance of nutrients & hormones in their body.
    I do believe that the long standing doctor suggested balance of a number of nutrient calories should be determined by the persons height,skeletal structure,
    genetics & active life style.
    With this I've always know that we should eat only what we need ( not less ),
    but stop when you know you are no longer hungry.
    Unfortunately there have been too many years that restraurants piled huge amounts of food on a plate & people got used to this, which is so unhealthy.
    Lean is better, but not CR which is too low in calories for optimal body functions is my opinion. Calories should be nutrient densse & you will eat less naturally.

    Posted by: Robin at January 12, 2014 4:19 PM

    Reason,

    Do you know if I have to be consistent with my CR diet? For example, half my week is split up into "exercise days" with normal caloric intake, and the other half of the week is "CR days" where I do not exercise for the day but try to intake less calories. And they are split up as every other day such as: Monday (exercise), Tuesday (CR), Wednesday (exercise), ect.

    My question is whether I have to do CR everyday to reap the benefits versus what I am doing now? It is pretty hard to run a few miles on the "exercise days" and then go home and starve myself.. Otherwise, my "CR days" consist of me doing my work on the computer and not getting up and moving around if not necessary. I am wasting my time with my current regiment?

    Posted by: Donald at January 29, 2014 4:11 PM

    @Donald: No-one knows the definitive answer to that and many similar questions. You might look at posts on intermittent fasting to see where the boundaries of the known lie for this sort of thing:

    https://encrypted.google.com/search?q=site%3Afightaging.org+intermittent%20fasting

    Otherwise, you might take these questions to the Calorie Restriction Society mailing lists - they've spent many years chewing over these and other questions, and will no doubt be able to provide some helpful insight and references.

    http://www.crsociety.org/
    http://lists.calorierestriction.org/mailman/listinfo

    Posted by: Reason at January 29, 2014 4:25 PM
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