Caloric Restriction

There is one issue I would like to discuss separately, which is calorie restriction. There is a recent body of research that strongly suggests we have the ability to slow down aging-to extend both life and youthfulness-through calorie reduction.

Why do you separate this discussion from the chapters that discuss nutritional issues?

Because the evidence for this school of thought is still preliminary, and I want to contrast this with the other issues for which the evidence is overwhelming. The evidence for the health benefits of a diet that is low in fat, cholesterol, and sodium and for the benefits of regular aerobic exercise is a rich mosaic that includes extensive human studies. The evidence for the benefits of restricting calories is based on animal studies. The animal studies are dramatic and have been totally consistent across many different species, so I feel they are worth discussing.¹ On the other hand, I do want to contrast the primary guidelines of the 10% solution (low fat, etc.), for which we have conclusive evidence, from this somewhat more speculative issue.

Fair enough. First of all, what is the calorie restriction program suggested here?

The Animal Experiments

Let me describe the rat experiments that have been conducted. The control group was fed a normal diet and lived a maximum normal life span, of approximately one thousand days. Typically, the control rats died from the deterioration of their hearts, kidney disease, or cancer. The experimental group had a restricted diet which consisted of about one-third fewer calories than the control group's diet but otherwise contained adequate nutrients, including vitamins, minerals, protein, essential fatty acids, and so on. They lived for about 1,500 days, or 50 percent longer.² I have to stress that this is a very dramatic and unusual finding. It has been consistent over many studies.

Of at least equal significance was the slowing of the aging process. Not only did the low-calorie rats live longer, but they largely avoided the feebleness, poor health, sluggishness, and grizzled appearance that accompanied the old age of the normal-eating group, even toward the end of the extended lives of these low-calorie rats. For example, the coats of the normal-eating rodents, which are smooth and white early in life, typically turn gray and oily by 24 months of age. The low-calorie rodents, in contrast kept their fur white and shiny for 40 months or more. Maze experiments showed that the low-calorie rats were significantly more successful at running mazes than normal-eating rats of the same age. Rates of diabetes and cataracts and the strength of the immune system were all dramatically better in the low-calorie rodents. Long after the normal-eating rats had died, the low-calorie rats continued to have shiny coats, very low rates of cancer and other diseases, and the higher levels of energy and responsiveness associated with youth. When these low calorie rats did die, they often appeared to do so of no obvious cause. According to Dr. Edward Masoro, a physiologist at the University of Texas Health Science Center in San Antonio, "When we look inside them, they're completely clean."³

Other experiments have tried exposing both groups to high levels of carcinogens. The low-calorie rats have shown significant resistance to the introduced cancer-causing chemicals, whereas the normal-eating rodents easily succumb.⁴ Even strains of rats that are specially bred to be prone to cancer, autoimmune conditions, and other diseases gain significant protection from a low-calorie diet. Dr. Richard Weindruch, a gerontologist at the National Institute on Aging in Bethesda, Maryland, comments that "any kind of screwed up animal seems to benefit from caloric restriction."⁵

There have been many experiments conducted on rats and on a wide range of other animals, all with consistent results. The low-calorie animals live significantly longer, generally about 50 percent longer, they age more slowly, and are generally much freer of disease even toward the end of their lengthened life spans.

Why does this work? I mean, what is going on here?

The Mechanisms

That is a very good question. The evidence provides some important pieces of the puzzle, but no one has a complete picture yet. One issue is the level of glucose in the blood. The low-calorie animals have significantly lower levels.⁶ This results from the fact that the low calorie animals burn glucose for fuel at the same rate as the normal eating animals, but with less caloric intake there is less unnecessary glucose left over. It is well known that free-floating glucose can have a variety of harmful interactions with essential proteins and enzymes. It is generally accepted that a lower serum glucose level is beneficial.

Another important issue are the so-called free-radicals, highly reactive oxygen molecules that are a by-product of the metabolism of food. These molecules cause a gradual deterioration of body tissues, particularly fragile cell membranes. Many researchers on aging attribute many or even most of the aging processes to the gradual deteriorating effect of oxygen free-radicals floating in the blood stream.⁷ The low calorie animals have substantially lower levels of oxygen free-radicals (which result from less food metabolism) and correspondingly less oxygen damage to cell membranes. Researchers have also discovered that the levels of a liver enzyme that detoxifies free-radicals are about 60 percent higher in the low-calorie animals.⁸

Other researchers have discovered that the low-calorie animals have more robust DNA-repairing enzymes. Deterioration in the DNA code causes cancer and accelerates other aging processes, so the greater effectiveness of these enzymes would account for the slower aging and lower rate of tumors in these animals.⁹

It has also been noted that the low-calorie animals have slightly lower temperatures, indicating a lower rate of metabolism.¹⁰ It is, after all, the "fires" of metabolism that raise the body's temperature. Metabolism clearly causes gradual damage, so a lower rate of metabolism will cause a lower rate of such damage.

It certainly makes sense that a lower rate of calorie consumption will result in a lower rate of food metabolism.

The Number of Calories in a Lifetime

Yes, that does make sense. And it is interesting to note that the total lifetime quantity of food eaten by the low-calorie animals and the normal-eating animals was roughly the same. The low-calorie animals ate approximately two-thirds as much food per day and lived 50 percent longer, so the total amount of food eaten over the life span was about the same as that of the normal-eating animals.

That would suggest that there is a certain number of calories allocated per lifetime, and if these calories are eaten more slowly, the result is a longer life.

That is the suggestion, which is intriguing to say the least. To look at it another way, the indication is that the clock of the aging process is not governed by the passage of time, per se. That is, we do not age with the passing of each minute, but rather with the consumption of each calorie. This is consistent with the view of living cells as heat engines. Another way to view this is to say that it is our "mileage" that causes aging and deterioration rather than the number of months lived, where mileage in this instance refers to the consumption of fuel.

So if an animal were to eat, say, one-third as many calories as another animal, it would live three times as long as the other?

No, there is a limit to this approach because of the other requirement I mentioned, that of obtaining sufficient nutrients. Without adequate vitamins, minerals, protein, and other nutrients, a human or other animal will become ill and ultimately die if the deficiency is not reversed. It appears that at least in the case of animals such as rats, the optimal level of calories for longevity is about two-thirds that of what the animals will eat if they are eating freely. Below that, it is difficult or impossible to obtain adequate nutrition.

There have not been any human studies?

There have not been any human intervention studies. Unlike the issues of lowering fat and cholesterol and increasing aerobic exercise, the issue of lowering caloric intake has not yet had extensive human experimentation. However, the animal studies have been remarkably consistent across experiments and across species. There is a strong suggestion that the effect will remain consistent up the evolutionary ladder. We know from other scientific studies that effects that are this dramatic in rats and this consistent across other animal species do generally extrapolate to humans. That is why we rely on rat studies when it comes to testing carcinogens. We routinely ban carcinogens that cause cancer in rats without ever conducting human studies.

There have been some human population studies. For example, the people living in the Okinawa region of Japan have forty times the number of centenarians (people 100 years of age or older) than the northeastern prefectures.¹¹ Furthermore, they have very little serious disease before the age of 60. Okinawans remain active much longer than their peers in other regions of Japan. The primary difference in their diet appears to be a lower caloric intake.

So what would the impact on humans be?

If we extrapolate the animal studies to humans, some researchers have estimated that the maximum life span of humans might be extended from 110 years to 150 or more.¹²

But very few of us live to 110 as it is.

This is true. These estimates refer to a theoretical maximum potential life span. Perhaps of greater significance, however, is the implication that by eating a diet that is low in calories and otherwise healthy, we are more likely to live out whatever potential we do have.

Are there any disadvantages to caloric restriction?

A Cautionary Note

There is one cautionary note I would like to make. There is evidence from the animal studies, and also preliminary research with humans, that excessive restriction of calories can cause a preoccupation with eating. This can trigger an eating disorder or other neurotic behavior.

I imagine people or animals significantly curtailing their eating must be hungry.

Yes, exactly. And hunger is a condition that you definitely want to avoid. Avoiding feelings of deprivation is both a goal and a guideline of the 10% solution. It is a goal because we desire a life-style that is satisfying and fulfilling. It is a guideline because the program will not be self-sustaining if you are hungry all the time.

As it turns out there is synergy between the low-fat orientation of the 10% solution and caloric restriction. Eating foods that are low in fat and high in fiber allows you to reach a state of satiety with far fewer calories than eating the foods that make up the normal American diet. But I am strongly opposed to reducing calories below the point at which you have satisfied your feelings of hunger.

You seem to be giving me a mixed message here.

That is a fair statement, and probably another reason why this chapter is not located in the front of the book. The mixed message is the following. There is considerable evidence that calories do count. Eating excessive calories has a negative impact in terms of both decreasing longevity and speeding up the aging process. Conversely, restricting calories up to a certain point appears to slow down the aging process.

On the other hand, any program that requires continual deprivation will ultimately fail and is likely to have negative behavioral consequences. Even when you are losing weight, I recommend that you eat a sufficient number of lower-fat calories so that you are never hungry.

So just what do you suggest?

The Guideline

Again, the evidence for the wide-ranging benefits of eating a diet that is 10 percent calories from fat and low in cholesterol and sodium, obtaining regular aerobic exercise, and following the other guidelines I have called the 10% solution are overwhelming, and I strongly recommend them to optimize health and well-being. The evidence for caloric restriction is not yet as extensive. However, it may take a long time before we have a comparable level of evidence. After all, the evidence for a low-fat, low-cholesterol diet has been accumulating since World War II, which is almost half a century. You may not want to wait that long before considering this issue. On the other hand, keep in mind the strong proviso that you must obtain adequate nutrition, and there is a real danger that a long-term program of caloric restriction may lead to a nutritional deficiency. There is also the issue of avoiding feelings of hunger that I discussed earlier. There are, of course, many poor areas in the world where people eat a low calorie diet because that is all they can afford. In general, these people are not obtaining all the nutrients they need. Needless to say, the poverty causes other problems, in that the food the people have available tends to be high in pathogens, and there is generally very inadequate health care, if any.

Having said all that, what I would recommend, and what I am doing personally, is reducing caloric consumption to a level that enables me to maintain a weight that is approximately 95 percent of my ideal weight. My wrist measures 7 inches, so according to table l in chapter 5, "Your Weight," I have a medium frame but am at the top end of that range. Since I am 5 feet, 6 inches tall, my ideal weight according to table 2 is 147 pounds. I maintain my weight at 95 percent of this figure (140 pounds) by eating about 2,100 calories per day and exercising an average of 350 calories per day.

Now you're talking about controlling weight. I thought we were talking about restricting calories.

They are essentially equivalent. Each calorie level corresponds to a maintenance level for a particular weight. For example, when I weighed 188 pounds, my maintenance level was approximately 2,900 calories per day. Now, at 140 pounds, my maintenance level is about 2,150 calories. If I were to eat 2,900 calories per day, my weight would rise and eventually stabilize back at 188 pounds. At 2,150 calories, my weight has stabilized at 140 pounds. Not surprisingly, one's maintenance level at a particular weight is roughly proportional to that weight (i.e., as your weight goes down, your maintenance calorie level goes down, too, by roughly the same percentage).

Thus stabilizing your weight and stabilizing your food consumption (and exercise routine) are essentially equivalent.

And you follow the other recommendations of your 10% solution?

Of course.

So what are you trying to do, live to be 150 yeas of age?

First of all, the research suggests that the benefits of caloric restriction on aging start when you start the caloric restriction, so there is a difference between starting at age 40 and starting much earlier in life.

But I am less concerned with how many years I will live than with the quality of those years of life.

So how exactly would you state this guideline?

I would recommend maintaining your weight at approximately 95 percent of your ideal weight indicated by tables 1 and 2 in chapter 5. You can estimate what your maintenance level of calories should be for this level by table 3 in chapter 5, but keep in mind that everyone's metabolism is different, so you will have to adjust this figure from experience. That is why I have stated the guideline in terms of weight rather than calories. Expressing the guideline in this way automatically takes into consideration your rate of metabolism. Also, you should have little difficulty avoiding feelings of hunger with this guideline. I strongly recommend, however, that you do not allow your weight to fall appreciably below 95 percent of your ideal weight (as indicated by table 2).

The content of the diet should obviously follow the guidelines of the 10% solution. Blood glucose levels and the level of oxygen free radicals are also reduced by eating a diet that is low in fat and high in fiber. Eating a diet high in natural grains, vegetables, and fruits will also assure you that you are obtaining adequate nutrition. It is important to eat a varied diet to make sure that you are getting all of the vitamins and minerals you need.

There is only one problem I have with this guideline.

What's that?

While eating a diet that is low in fat, cholesterol, and sodium may appear at first glance to involve a sacrifice in palatability, you have strenuously pointed out that this is ultimately not the case. You have repeatedly indicated that once you discover the variety of foods that do comply with these guidelines and once your tastes adjust, the 10% solution represents an enjoyable and satisfying way to eat. So there is no real sacrifice involved.

Yes, that's true.

But with this guideline there is a sacrifice. You have to eat less.

But consider that if aging is indeed governed by metabolism, which is to say that we have a certain number of calories to eat in our lifetime, and assuming that our life is not cut short by an accident or other unpredictable event, then it would make sense to eat somewhat less each day and thereby enjoy a longer life. After all, there are many other enjoyable things to do in life besides eat.

Eating is right up there, I have to tell you.

I'll grant you that. I have always loved to eat and still do. I would make two points here. First, the potential is not just to extend your life in terms of number of years, but to make those years healthier. All of the guidelines of the 10% solution, including this one, are intended to make those years more fulfilling. Second, I still eat a reasonably large quantity of food. While 2,150 calories may seem limited on a "normal" high-fat diet, on a diet that is only 10 percent calories from fat it is a rather significant quantity. As I pointed out earlier, low-fat food goes a lot further in terms of quantity for the same number of calories. I am never hungry and eat three satisfying meals a day.

Do you want to explain the title of this chapter?

The first "fountain of youth," if you will, is the set of other guidelines we have been discussing: 10 percent calories from fat and so on. The evidence that such a life-style will delay or even eliminate most of the diseases and other conditions that are normally associated with aging has been growing substantially for half a century. The issue of caloric restriction is now the second major approach to extending mortality and delaying morbidity that has gained some level of scientific corroboration.

So spend your calories wisely.

Yes, indeed.

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