In literally thousands of experiments, on a wide range of animals (almost certainly to include humans!), calorie restriction has greatly extended maximum and average lifespans and improved disease resistance, including resistance to many cancers. There is still uncertainty about why calorie restriction has these desired effects. Two important reasons proposed for the benefits of calorie restriction are: 1) fewer calories mean that there will be a reduction in the accumulation of oxidant and free-radical damage, and 2) fewer calories alter fat deposition, obesity, and hormones. The practical effect of this is improve the immune response of calorie-restricted (hereafter CR) animals.

There are numerous reputable websites to learn more about the underlying animal studies (preliminary corroborative results are now coming out on the rhesus monkey experiments currently underway). Indeed, there are already convincing studies demonstrating the health benefits (and, no doubt, the longevity benefits…though not enough time has passed to observe these!) in humans.

For present purposes, that CR—with adequate or optimal nutrition (the first controversy)–is good for your prospects for a long, healthy life will be taken as a given. The science is unambiguous and the life extension benefits have been known (surprisingly) since 1935. The interesting questions revolve around related issues.

What is Calorie Restriction?

You might (in an ideal world) want to get an extensive blood test, so that you can verify for yourself the benefits of CR as they occur. Also, in an ideal world, you would want to calculate how many calories you are currently eating. This will add some useful precision, if others are to learn from your experience with CR—remember that you are a pioneer and that leaving a record is a good thing. But, unfortunately, I did not do the latter, so I have only a loose understanding of what percentage of CR I am engaged in at any particular time.

The range of recommended calorie restriction levels is from 10% to 25% from the unrestricted diet (Walford believes most people should start CR with 1,800 to 2,200 calories per day). But, you don’t want to lose too much weight and you don’t want to lose it too fast! A number of ways of thinking about CR have emerged. If you feel weak, lightheaded, or are overly tired and sleep a lot, you are either losing too fast or not getting enough nutrition with your reduced caloric intake—you should feel better, not worse, if things are going right.

To give a reference, it would be difficult for most people to lose more than a pound a week of true weight (ignoring water) in a healthy way. Since a pound loss (3500 calories, roughly) in a week breaks down to 500 calories per day, that is a quite substantial restriction (16.7% CR if one is initially at 3,000 calories a day, which is plenty of food). Note that the “Percent Daily Values” on all of the food packages these days refer to a 2,000-calorie diet, with gram numbers also being given for the 2,500 calorie diet. If you were eating at those levels before restriction, losing one pound a week would be 25% and 20% CR respectively.

So, you are “safer” to take six weeks to lose 6 pounds, though this, too, is likely to vary with the individual. When I lost 12 pounds in that time (2 per week), I felt very bad, but Ray (another CR Society member) lost 15 pounds in 6 weeks and felt fine. The key is to be guided by how you feel–you are supposed to feel better, not worse. If you feel worse, lose more slowly. Remember that when you are losing fat you are also losing muscle along with that fat; you may also be releasing toxins stored in fat too rapidly.

Also, and especially if you are moderately to very active, you will find your fat percentage declining steadily as you lose weight. Walford believes that you should not let that fall below 6-10% for men and 10-15% for women. This is not terribly likely to happen for most people on CR—the 1990 mean values for males between 40 and 75 years old varied from 25.3 to 26.8% while the female means were 34.9 to 39.0% for those age groups! For men between 40 and 75, a 13 to16% body fat will put you in the lowest 5% of the nation, while for women, a 25 to 28% body fat will also make them leaner than 19 out of 20 people!

And, we’ve gotten a bit fatter since 1990. So, it’s not too likely that you will acquire a dangerously low fat percentage. Despite Walford’s warning, having quite low body fat percentages may not be so terribly undesirable at least for particular individuals (Frank Shorter was estimated to be only 1-3% fat when he won the Olympic marathon in 1972!).

A rough measure of how fat people are is the Body Mass Index or BMI. This can be calculated by dividing your weight in kilograms (2.2 pounds to a kilogram) by the square of your height in meters (39.4 inches to a meter). Thus, if you weigh 150 lbs. (68.2kg) at a height of 5’9″ (69″ or 1.75m) tall and weigh 150 lbs., your BMI is 68.2kg/3.0625 = 22.3. Traditional nutrition/health sources say that the BMI for “normal” men and women should be in the range of 20-27, which roughly corresponded to the 10th and 75th percentile values in 1971-74. For a flavor of where you stand, from 1990 data (we’ve gotten fatter since then!)

Women generally have lower BMIs, except among the very obese, where there are more women than men. The reconciliation of these BMI data with the earlier data that indicated that women have higher fat percentages (true at every BMI) than men comes via the greater amount of lean body mass among men. I would guess that the average BMI of the members of the CR Society (a newsgroup on the web) would be well under 21, with many as low as 17. A recent study has indicated that those with lower BMIs are much healthier and less prone to disease and premature death than those with high BMIs.

While perhaps a depressing revelation for many, it turns out that you do not get CR’s health benefits by losing weight via increased caloric expenditure. It is true that a typical person could lose 1 pound a week either by restricting calories an average of 500 per day or by running 5 miles every day (losing an average of 100 calories per mile more-or-less regardless of speed) and eating the original number of calories.

The reason exercise does not give CR benefits even if it gave equivalent CR weight stems from how CR is hypothesized to work. Food is the source of 90% of the oxidants or free radicals in the body—reducing food reduces oxidative damage. Exercise, ironically, actually contributes to free radical formation by burning that food faster. These negative effects are for most people (the non-CRers) more than offset by the health benefits of exercise, so that average lifespan is certainly increased by exercise. [Probably the oxidative damage is more than offset by positive effects of improved fat deposition, reduced obesity, and improved hormone status.] But a number of rodent experiments indicate that exercise doesn’t add anything to the maximum lifespan and fairly little to the average lifespan when animals are already calorie restricted.

It is the CR that gives the benefits—exercise to feel better and to maintain independence in old age, but don’t exercise as a substitute for calorie restriction. Note, too, that while CR won’t make you stronger, it will make you relatively stronger—you’ll be able to do more push-ups and chin-ups, for example, just because you have less weight to lift! These benefits will be manifest in everything you do as you move around in your lighter body throughout the day.