Calorie Restriction with Optimal Nutrition (CRON)

by Christine on May 4th, 2010

filed under Diet, Food, Nutrition, Eating Disorders, Gastric Banding Surgery, General Information

Calorie Restriction with Optimal Nutrition (CRON) is a dieting lifestyle that focuses on nutrient-rich, very low-calorie diet.  The science behind this lifestyle diet was developed by Roy and Lisa Walford and Brian Delaey. The goal of the CRON diet is to improve overall health and slow down the aging process.  This diet is commonly referred to as the “Longevity Diet.”

I am personally not an advocate for following fad diets.  I have tried most of them in the past: Weight Watchers, Jenny Craig, Nutri-System, Atkins, South Beach, Master Cleanser, etc.  Most of these diets may help you lose weight (most didn’t even do that for me), but as soon as you stop using that diet, the weight comes right back on – usually in surplus.

However, because of the gastric banding surgery, I think it’s safe to say that I follow a CRON-based diet just by happenstance.  I don’t subscribe to a CRON lifestyle, and this blog isn’t about CRON, but if you think about what I do in terms of nutrition, then the basic tenements are the same. This isn’t a diet to me, this is a lifestyle.  There’s no getting “off” this calorie-restrictive diet for me; this is pretty much it for life, and that is okay.  I typically eat approximately 800 calories per day. This is very low in calories – too low for most people. However, for me, assuming that I choose healthy foods that give me all the nutrients that I need, this is enough energy (calories) not just to get me through the day, but to give me energy to exercise as well. A great side effect of this is that following a calorie restrictive diet helps me to lose weight and reach my optimal weight.

I’m not advocating that everyone pick up and follow a CRON-based lifestyle. This isn’t for everyone. But I believe that a CRON-based lifestyle may be a good choice for many people, including those trying to find a way to overcome eating disorders. For example, for an anorectic, eating a low-calorie diet may appease the demons battling in his or her head, but eating a nutrient-dense daily diet may also keep that individual healthy. For a binge eater, following a CRON-based lifestyle may provide a strict enough daily regimen to keep from overeating.

How does it work?

The underlying belief is that each individual person has what is called a “set-point,” or a weight that is specific to each person, that is his or her healthy weight.  Consequently, abiding by the USFDA guidelines of 2,000 calories per day may work for some people, but not for many others.  This idea of an individual “set-point” is more similar to the Basal Metabolic Rate (BMR) concept.  Some proponents of the CRON diet believe that this calorie set point is 10-15% under the “set point.”

Followers of the CRON diet typically recommend following a restrictive intake of 20% less than you would have eaten normally, although other proponents suggest that 20% less than your BMR would be more appropriate.  If you are considering starting off with this, start by reducing your calories by 5% and then decreasing the calories from there, slowly, as your health allows. Don’t go below 16% restricted calories.

The average American eats 2445 calories per day. A “typical” CRON follower consumes about 1671 calories per day.  Sixteen hundred is still a lot – nearly double what I personally eat. CRON is not about starving yourself. In many ways, the CRON lifestyle is similar to the Okinawa diet: Hara Hachi Bu: Eat until you are 80% full.  (

Exercise is also very important to the CRON diet. However, the more you exercise, they more calories you will need to consume. Using computerized software (see below in the resources section) can help you factor in all these issues to figure out what your optimum calorie intake should be.

It’s important to emphasize this point: CRON is not about starving yourself. If you’re hungry and starving, then eat something.  If you are eating nutrient-dense foods, you shouldn’t be feeling hungry. If you are experiencing hunger, then you should probably re-evaluate the foods you are consuming, the amount of exercise you are doing, etc.  One CRON follower says, “Hunger does not have to be an issue; many people on CRON actually struggle to eat 1500 calories a day – feeling too full!” (  I can personally attest to this: I eat all day long, and I eat when I’m hungry.  I’m a healthy, functioning individual, and I only eat about 800 calories a day. Again: don’t starve yourself.

To get started, you need to evaluate your biomarkers. Find out more information about these tests by visiting this site:

What can I eat?

Food choices are of the utmost importance in a CRON diet.  It’s essential to choose high-nutrition foods, with the right quantities of protein, fat, carbohydrates, vitamins, minerals, fiber, and probiotic bacteria. The CRON diet recommends approximately 30% protein, 30% fat, 40% carbohydrate, which is a ratio similar to the Zone diet.

Walford recommends “nutrient super-chargers,” such as:

  • Kombu
  • Brewers yeast
  • Wheat bran
  • Wheat germ
  • Shiitake mushrooms
  • Non-fat dry milk
  • Soybeans
  • Tofu

Other CRON followers suggest:

  • Vegetables, especially low-calorie and high-fiber vegetables.
  • Fruit
  • Small amounts of lean meat
  • Fish
  • Nuts
  • Beans
  • Egg (white)

Luigi Fontana, MD, Ph.D., assistant professor of medicine at Washington University St. Louis says that the calorie restriction diet resembles a traditional Mediterranean diet.

Again, I don’t profess to be a CRON follower, per se, as stated previously. But when I look at these foods, this is what I eat! Lots of beans, nuts, fish, lean meats, vegetables, eggs, and sometimes some fresh fruit.

With a CRON diet, you should avoid sugars, simple flour/carbs, and fried foods. Well, that makes sense, doesn’t it? That’s hardly a revolutionary concept.

The calorie restrictive diet must contain appropriate amounts of Vitamin D, calcium, phosphorus, protein, and trace minerals to maintain healthy bones.  Most people will probably need to consider a dietary supplement to avoid vitamin deficiencies.

When should you eat?

I can personally attest to the benefit of “grazing” all day long. I eat between 6-8 small meals each day, consisting of 100-150 calories per “meal.” Consequently, it’s more like I snack rather than eat a meal.  This method has several benefits: (1) I don’t typically have a glucose high followed by a crash, like I would typically after eating a big meal.  My energy is sustained throughout the day. (2) I eat when I’m hungry. I don’t eat when I’m not hungry. This has helped me overcome binge-eating in a very drastic way, although finding the right cut-off point (aka, “I’m not hungry anymore, so I’m going to stop eating even though I still have almonds left in this package”) is sometimes difficult.  (3) It’s easier to eat healthfully when you eat in small doses.  Because I don’t really ever eat a large meal, I don’t eat crap foods like pasta or pizza. Instead, I find I eat a lot more fruits, veggies, nuts, and fish partially because they are lower in calories and meet my “snack-grazing” methodology a lot easier.

Contrary to this eating-all-day-long methodology, some studies have shown that eating every-other-day (called “intermittent fasting”) has shown beneficial effects, such as reduced serum glucose and insulin levels.

Walford recommends that CRON dieters eat three nutrient-dense meals per day.

What should I weigh?

According to Walford, losing weight until a BMI of less than 20 is reached is optimal. (Walford 2000)  This is the level that, when mortality rates have been analyzed, that shows the most promise for longer lifespans and less health-related problems. However, it’s important to note that while this very low BMI is seen as “optimal,” several studies have indicated that this low BMI may actually be damaging for naturally-lean people who have minimal amounts of body fat.  Furthermore, the suicide rate is higher for men with BMIs less than 21 than those with higher BMIs.  Consequently, this particular topic is still under scrutiny. However, this much is clear: being overweight or obese significantly shortens one’s lifespan.

If your BMI drops below 18.5 or your body fat reaches below 5% male/8% female, then you’re probably close to the limit. Pay careful attention that you don’t go too far below this point.

What are the life benefits?

Research has indicated that by following a reduced calorie diet, life expectancy may increase. This has been proven based on many animal studies. Scientific study has shown that “several genes in the sirtuin class, including SIRT1, SIRT3, and SIRT4, create enzymes that increase the activity of the mitochondria and slow the cell’s aging process.” (   I’m not an expert in the field, but I think that’s geek talk for this idea: when the metabolism slows down, the body likewise slows down the aging process.

Studies also show that following a calorie-restrictive daily diet will stunt growth (body mass).  Although no human studies have been completed up to this point, preliminary evidence suggests that a fully-grown human adult that has been raised on a 40% calorie restricted diet since 2-3 years of age would weigh about 75 pounds instead of the normal 150 pounds. Presumably the same human could live until about age 120. Again, this is unproven up to this point.  For an average adult (like you reading this report) adopting this calorie restriction lifestyle, you may only prolong your life by 5-10 years, maybe less.  Whether that’s “worth it” to you in the long run is for you to judge.

The studies aren’t all good. There are indications that an adult shifting to a 40% calorie restricted diet would be very dangerous.  16% is the maximum reduction in BMR for metabolically active tissues obtained by starvation diets; consequently, a calorie restrictive diet not exceeding 16% may be considered safe because the metabolism can adjust to the lower calorie intake without causing structural damage to the body (such as bone loss, muscle loss, etc). (Keys et al 1950)

Benefits also include decreasing the risk of heart attack, stroke, diabetes, and cancer. Benefits also include a stronger immune system, increased fitness, and greater appreciation of food.

What are the risks?

Scientists have discovered that adults adjusting to a CRON diet with a severe cut in calories may actually shorten their lifespan. Make sure that any calorie cuts are done slowly over time, and only as your physical health allows.

If you find that you are feeling lethargic and tired, then you need to either increase your calories or choose more nutrient-rich foods.  A recent study published in the American Journal of Physiology – Regulatory, Integrative and Comparative Physiology found that decreasing calories decreased the amount of activity expended. This should not be the case. If you find yourself doing less, then re-evaluate and eat more.

What is the difference between CRON and Anorexia?

The CRON diet advocates for longevity, optimum health, and delaying the onset of disease. Anorexia is characterized by low body weight and a fear of getting fat. Anorectics typically aim to be thin at any cost, even at risk of one’s health. CRON followers want to maximize their physical health, regardless of the exact body weight achieved.

Free Software

The CRON-O-Meter is a free, open source, and cross-platform dieting software. You can download it by visiting this link:

The Interactive Diet Planner (DWIDP) is created by Roy Walford, the scientist behind this dieting theory. Windows Only. Free demo version is available at

This is a free online Calorie Restriction Calculator:

More resources and works cited

BMR Calculator:

A thorough article about the CRON diet.

Keys A, Brozek J, Henschel A, Mickelsen O, Taylor HL. The biology of human starvation. Minneapolis: University of Minneapolis Press, 1950.

Roy Walford, M.D. Beyond the 120 Year Diet: How to Double Your Vital Years. 2000.

Weindruch R, Walford RL., “Dietary restriction in mice beginning at 1 year of age: effect on life-span and spontaneous cancer incidence.” Science, March 12, 1982; 215(4538), pages 1415-8. PMID: 7063854

McGlothin, Paul and M Averill. The CR Way: Using the Secrets of Calorie Restriction for a Longer, Healthier Life.

Calorie Restriction Recipes found online at:

Blog of a lifelong CRON follower:

Another blog of a lifelong CRON follower. Includes some Youtube videos:

Press release about CRON.

Doctor OZ interviewing followers of a calorie restriction diet:

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  • Lenny Trivitt

    Its my firm belief that overhyped weight slimming solutions are not good long term solutions. Selecting your food wisely and exercise is always the best solution to cut down your fat.

  • Lenny Trivitt

    Its my firm belief that overhyped weight slimming solutions are not good long term solutions. Selecting your food wisely and exercise is always the best solution to cut down your fat.

  • Hayden Robertson

    research suggest that calorie restriction can also lengthen a person’s life span`~,

  • Hayden Robertson

    research suggest that calorie restriction can also lengthen a person’s life span`~,

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  • Paul

    Christine you look terrific! Congratulations on all you have achieved with CR.

    Do be careful about egg whites and brewers yeast. We loved them too when we first started, until we saw what they did to IGF-. Some studies show elevated levels of this growth hormone to be associated with increased cancer risk.

  • Matthew Lake

    Hi Christine! :) I am the owner of “matts-cr”. I’ve since moved to – is it possible you can update the link? And thanks for linking to my site, I really appreciate it! :)