Food For Thought: An Interview with Nutrition Scientist Dr. Paul Saltman

Department of Biology, University of California, San Diego, CA, USA

We are barraged by the media with endless claims and promises about the value or risks of what we eat and drink and what we take in the way of dietary supplements. Where is the science? I spoke with nutrition science authority Dr. Paul Saltman, professor of biology at UCSD, and author of various texts and popular books about the science of nutrition, in an effort to separate some nutrition facts from food fiction.

Q: We hear so many claims and promises about what's good for us and so many pronouncements about what's bad for us to eat. How can a person bring a scientific approach to the task of sorting through all this information?

A: I have a basic premise when I teach about food and nutrition. Food is metaphysics. What we eat, when and how much, has much to do with our culture and religions, our economic and social environment, with our age and lifestyle. Although it provides the nutrients by which we live, food is not in itself a science, it is a sensual experience required for survival.

Nutrition, in contrast, is an exact science. It is experimentally verifiable through the strategies of what is known as total parenteral nutrition (TPN), i.e. intravenous feeding. With TPN feeding all of the nutrients that a human being needs from the time of infancy to the latter years one can be maintained alive and well and growing without ever eating a morsel of food or drinking a drop of liquid.

This is the science. We know there are 44 chemical nutrients required for TPN. We understand what their chemistry is and what their structures are. There is nothing esoteric or magic about it. These nutrients are not kosher, not Szechuan or Cantonese, not chocolate or vanilla, they are chemicals. These 44 chemicals really constitute the true staff of life.

Q: Humans have evolved relatively rapidly from a caveman existence to the world of today. Can we learn anything about human nutrition by looking at what our prehistoric ancestors ate? For example, some people like to claim that we evolved while eating a diet primarily composed of forage.

A: There is good news and bad news. Those of us that have the luxury of adequate nutrition and supplies of clean water and the ability to get rid of our wastes have a longer lifespan and better health than do those who are less fortunate. We've learned about agriculture, public health, even about medicine. The bad news is that, in the developed nations at least, when you have ample supplies of inexpensive foods that taste good, we get obesity and the consequences of obesity, which are enormous.

We have evolved. The Pima Indians evolved to meet the needs of living in the desert. In their case genetic selection was for those with the most effective metabolism and ability to conserve scarce resources. Make available a 7-11 and a six pack of beer to people with this genetic background and you've got people who are very obese and very sick from heart disease and diabetes.

We are living longer and reproducing more. We have challenged the planet because of the growing population, using energy and resources in a way which frequently becomes deleterious, but need not be. The issue is how do we balance this well being from man commandeering the world versus the needs of the roughly two-thirds of the population that do not get enough to eat.

The cave-man model of the primal vegetarian diet makes no sense. It is Rousseau's notion of the noble savage. It is nonsense. We should go back even before man, to chimpanzees. It is often said that these beautiful primates, precursors of humankind, are vegetarians. They are not. They love meat. Indeed, recent research shows they will really hunt to get meat, and using a human analogy, will use meat to beg for sex. We did not evolve from a vegetarian culture. We became less vegetarian and more dependent on meat in our diet as a consequence of being able to raise via animal husbandry, animal sources of protein.

I believe obesity is the root cause of many forms of cancer, heart disease and stroke and many other aspects of human disease. But we are living longer now with our current diet than Cro-Magnon ever did. The reason Cro-Magnon's didn't have a lot of cancer is that they didn't live long enough to get cancer.

Q: Some of the first scientific understanding of essential nutrients came with the observation that a lack of certain nutrients was associated with some disease states, for example, scurvy. How has the study of nutritional deficiency contributed to the science of nutrition?

A:One of the first cases studied carefully was the case of polished rice and beri-beri in the Dutch East Indies. Dr. Eichman found that polished rice caused this terrible disease and that eating the rice polishings that had been removed would relieve the symptoms of the disease. That was a beautiful demonstration of a thiamine deficiency disease.

The subsequent isolation of the different vitamins led us to understand through the vitamins (one of only six of essential nutrients groups) some mechanisms of action of specific nutrients. This led to a way of looking at nutrition considering the mechanisms of water, calories, carbohydrates, fats, proteins, amino acids, minerals. This is a whole different way of knowing why and how these 44 nutrients are essential for the human organism to thrive grow and reproduce.

Vitamins are only part of the story. For example it is equally important that we understand the mechanisms of how calcium is used, how potassium and sodium are in balance in terms of electrolyte balance inside and outside a cell, and why magnesium is required, and how phosphate serves the body. These are every bit as important as knowing about vitamin C and its role as a co-factor in the hydroxylation reactions of proteins.

Q: Antioxidant vitamins get a lot of attention these days. Go into a vitamin store and you will see promises of eternal youth. But these promises are made on supposedly scientific grounds. What's going on here?

A: Let me say unequivocally. There is no unambiguous double-blind, prospective controlled experiment that show that doses of antioxidants greater than those required by the USDA allowances have any value as a protectors against disease, or as curative agents once a disease occurs, other than in the case of deficiency disease. The notion of mega-dosing popularized by Linus Pauling with vitamin C, has yet to be proven in an unambiguous fashion. That bothers me. If I believed that there was data supporting the use of mega-doses of antioxidants, I would be swilling E, and taking mega-doses of C faster than anyone. However, I don't see that data.

We know oxidative damage occurs in tissues. I've studied the role of iron and copper in nutrition. These elements are required for life. but in excess or bound in wrong fashion they can cause free radical damage. I believe vitamin C is an antioxidant but I also know it can be a pro-oxidant under proper circumstances and can cause extensive damage to cells and tissues.

Because I know that oxidative damage is bad doesn't mean that anti-oxidants are good over and above what has been found to be required in experimental studies.

Q: Will it ever be possible to answer these claims one way or another with scientific studies?

A: Yes, I believe so. Prospective studies with antioxidants are underway. Science requires repeatable experiments. If a nutrient is useful you will see an effect. We went down into Durango, Mexico with Mexican physicians and fortified the milk with iron and copper. We were able to demonstrate in controlled double blind studies that in children who didn't look anemic we could move hemoglobin concentrations 20% above where they started. This is a marked increase. We know the better your hemoglobin levels, the more oxygen you deliver, the better your myoglobins and cytochromes. This in turn produces better vitality, health and growth.

Q: The WHO has numerous programs to provide fortification and supplements of essential nutrients.

A: These programs have emphasized the importance of both micronutrients and macronutrients. There are good examples where adding nutrients such as amino acids and calcium have made a difference in public health.

Q: Calcium is a good example of complementary nutrients. It's not just a matter of taking calcium is it?

A: Prospective studies with calcium show that if women take RDA amounts of calcium it will increase bone density. Adding trace elements can add bone density for post-menopausal women. These are facts demonstrated by prospective studies. On the one hand, if women took 1000 mg of calcium per day with or without vitamin D they will increase bone density. But, women should also take vitamin D, fluoride, trace elements and get exercise. And if post-menopausal, women should consult a physician regarding hormone replacement therapy. All of these factors play a fundamental role in health and maintenance of skeletal tissue.

Similarly, iron is much more effectively used when taken with copper. If you add one copper for every ten irons, you can get by with a lot less iron. We also know that sugar, organic acids and other molecules in the diet enhance the uptake of the various metal elements.

Q: At the moment there is a new push at WHO to include long chain polyunsaturated fatty acids (PUFAs) in formula Q: fatty acids. LC-PUFAs and formula.

A: That is a small part of the fat problem. Infants need PUFAs. We all do. The issue with formula is that you want to mimic as much as possible what's in human mothers milk. Everyone in the pediatric community agrees mothers milk is the best way to sustain growth and development in the child. So with formula the issue is, if the mothers' milk has PUFAs, so should the formula.

Q: Fat is often portrayed as the enemy for adults trying to eat a healthy diet. Is fat all bad?

A: We live in world filled with fear of fats and cholesterol. People and organizations proclaim that 30% fat in the diet will make us healthy. Yet, when we go back to TPN, the IV bag can contain as much as 55% calories in fat. People receiving TPN do not get fat on this diet. They are not obese and don't have heart disease. The French diet is about 45% calories from fat, yet they have half the level of obesity, and half the level of heart disease of this country.

The physics of calories states that all calories are equal. That is a thermodynamic truth. A calorie from fat equals a calorie from carbohydrate.

So what's wrong with fat? Fat makes food taste good. When food tastes good, you eat more. Eat more calories you get fat. Obesity is the number one nutritional disease in USA. It is a disease of self-abuse, with more calories in the than out. If we eat more than we exercise, more than our basal metabolic rate can sustain. we suffer the physiological detriments from that obesity. If we could control obesity we would have major handle on one of the biggest panoramas of health problems in America today.

There is some confusion about PUFAs. We know that these essential fatty acids are required as precursors to make prostaglandins and related compounds necessary for cell membrane structure. In general PUFAs are said to make good fat, i.e. high-density lipoprotein, where saturated fats make the low density lipoprotein. Good guys, bad guys, we're back into metaphysics. The point is that some fatty acids relate to the balance between high density and low density lipoproteins. However, the most important issue is your total glyceride concentration in your blood stream. That is what correlates best with obesity.

Q: There are guidelines handed down from above on what constitutes a healthy diet. What is a rational person to make of these generalized guidelines?

A: This is a very complicated question. Part of me says bless the FDA and USDA for all of the research that has taken place in the 20th century. This research has brought nutrition to be an exact science and has given the term 'nutrition' meaning in this country in terms of developing the well being of the people. Whether you are talking about six basic food groups or four basic food groups, circles that look like peace signs or triangles and pyramids, the notion that people are concerned about the health of the nation is good.

But these guidelines have not been without problems. For example, George McGovern's committee formulating the 'Diet for a Healthy America' made terrible mistakes, scientifically as well as intellectually in terms of the belief that you can tell people what to eat and what to do and that's going to make them better, healthier people. It's important to remember that nutrition guidelines are made by committee.

Q: Can't the public can be excused for being confused when the government changes it mind every couple of years?

A: Yes, and the scientists change their minds too. These mixed messages leave us terribly confused and makes it even worse than before. This is why I'm doing the class. The level of illiteracy in America is so great that we haven't got enough knowledge to pose the questions properly and force the governments and responsible health groups to produce evidence for their claims. We believe the latest bumper sticker slogans, the latest dogmatic statements. When these start to get into conflict, people say the hell with all of it, I'm going to have a hamburger and a malt and french fries, or at the other end of the spectrum, bean sprouts and brown rice. What concerns me above all is to give people a level of science literacy so they understand where the science ends and the metaphysics begins.

This kind of grounding would allow people to make informed decisions about their own lives. People need to know the consequences of what they do, not believe in the magic of either the hamburger or the bean sprouts. With this knowledge anyone can make you own diet in your life that includes an integrated intake of nutrients as food and/or supplements.

I believe in supplements. I believe the government has made terrible mistakes in the past. For example, not recommending folic acid supplements to pregnant women. I think it is obscene when the government says food is the only way to get adequate nutrition. That's wrong. If they were right, you couldn't have TPN. Yes, it's right and healthful to have a good diet, if you make selections predicated on your age, your lifestyle, your sex and your genetics.

Q: Our lifespan and general health are determined by our genetic background, as are elements of our weight level and metabolism. How do recent discoveries about the "ob" and "fat" genes, and the gene product "leptin" contribute to our understanding of nutrition?

A: The genetics is not really new. Scientists have been studying genetically predisposed obese rats for 35 or 40 years, trying to understand what genes are at work and what the gene products are. It turns out there are at least five and possibly as many as ten or twelve genes involved. Do we know that there is a genetic component in human weight? Of course. Many twin studies have shown this.

The leptin research is fascinating. Leptin is the first gene product we've identified, and we're still looking for others. Now we need to find out if leptin affects satiety, basal metabolic rate etc.

The question is, what's going on here? There is not a diet for everyone. Rather, there is a diet for each one of us. There are an infinite number of diets within the space defined by the number of calories we need, adequate amounts of the 44 chemical nutrients we need, and our age, sex, lifestyle and genetics. Each one of these parameters is interdependent on each of the others.

If you are a bicycle rider in the Alps eating 10,000 calories a day, I'm not interested in how many calories a typical human should have each day, I'm interested in the needs of that bike rider. If you are sitting on a couch channel surfing, your calorie needs go down. Your basal metabolic rate changes with age. Your genes affect your basal metabolic rate.

QUESTIONS FROM THE ACCESS EXCELLENCE FELLOWS AND THEIR STUDENTS

Q: Some weight loss programs advise drinking several glasses of ice water, with the explanation that water increases the metabolism of fats. Is this true?

A: You burn fat with oxygen and release energy. If you drink ice water, a small (but potentially significant) amount of this energy would be used to raise the temperature of water to body temperature. Drinking water is good for several reasons. Water fills you up and so you don't eat as much. Water is zero calories, and it's good nutritionally to drink eight glasses of water.

Q: After aerobic exercise metabolism is said to be higher for a little while, is this true?

A: No question about it, it's true. The great benefits of exercise are in terms of weight management and cardiovascular health. When you exercise you require more calories, you burn more energy. As you raise your energy up with exercise, your body returns to its normal basal metabolic rate slowly, over a period of about two hours. Depending on how much you exercised, the amount of excess energy burned as this rate goes down, since you are continuing to burn calories even though you are resting. The most interesting aspect of exercise, not fully appreciated by coaches is loss of appetite. Really good exercise causes a loss of appetite. Top athletes often have a problem eating enough to restore calories.

Q: A teacher asks for clarification on how fat cells communicate with other tissues in the body, and whether some foods make your more fat than others.

A: The communication issue is not nearly as important as the thermodynamic issue. The first law of thermodynamics states "if you eat it and don't burn it, sit on it". You sit on these calories stored as glycerides in your adipose tissue. Some people have more fat cells than others, meaning some may have a tendency to store it more easily than others. But you won't store it if you haven't got it.

The notion that some foods are more fat-producing than others is true, but only over and above the line of how many calories you have to burn in order to maintain your basal metabolic rate. It takes more energy to store carbohydrates as fat. But we don't store much carbohydrate, less than a half a percent is glycogen. So you may get a little benefit by eating carbohydrates. The other thing is that carbohydrates fill you up, so you don't eat as much.

Q: Is it true when a person is exercising aerobically that they do not use up stored glycogen at the same rate as if they were exercising anaerobically?

A: Yes. The beauty of aerobic exercise in terms of burning calories is that the optimally trained athlete will burn 70% fat, 30% carbohydrates. But if you don't have the oxygen, you are forced into a glycolytic pathway in which you are forced to used carbohydrate stores, making your ATP by glycolysis, not having adequate oxygen in effect to burn the fats and carbohydrates through the Krebs cycle, which can generate 13 times more ATP than can glycolysis.

However, there are other athletic events, such as sprinting, that are anaerobic in nature. That is where you want to be able to use energy the other way. You train for different muscles and with different method.

Q: A teacher asks about claims made in best-sellers about antioxidants in terms of aging.

A: The evidence is clear that as animals age, there is a deposition of more end products of oxidative damage to cells, such as lipofuscin- a pigment that's made from lipids and lipid derivatives. Also your burden of mutations increases over time, and the repair mechanisms become less effective. But, to say that I'm going to live forever with mega-doses of antioxidant vitamins, there is no evidence for that. You will live longer if you are not obese and you exercise and don't abuse your body.

Q: There is a lot of interest in performance nutrition products geared towards athletes and would-be athletes. These power bars and super drinks often boast ingredients such as complex carbohydrates and amino acids that supposedly enhance performance. Is there any scientific basis for these products?

A: These are high priced goods. What are they selling you? Calories in the form of carbohydrates, fats, proteins, along with vitamins, minerals. You can get all of these in the supermarket. The best, cheapest amino acid supplement is dry milk powder.

Your body has never seen a complex carbohydrate in its blood stream. Every carbohydrate you have ever eaten has been broken down to glucose and absorbed. Just as sugars are broken down to fructose and glucose and absorbed. There is no difference. The only think is that when you eat complex carbohydrates you usually eat them with other foods and it fills you up. But there is also the metaphysics of food again. If you eat a power bar and you believe it will give you the mystical powers of the super athletes that are endorsing it, then you will play above the rim. It's part of psyching yourself up for an event.

If you are an athlete you want to make sure than your eating the nutrients that are in the TPN bag. Many athletes are actually low on calcium and low on iron. Why? Because their coaches say don't drink milk because of the mucous, and don't eat meat because of the karma. So where are they going to get calcium and the trace elements?

Q: A teacher who climbed Mt. Everest asks about the effects of high altitude on metabolism. The teacher reports experiencing reduced appetite and altered metabolism of what was eaten. Is the metabolism less efficient because of reduced oxygen?

A: Absolutely. Oxygen is required to burn the fuels of the body. The net result of this at low oxygen tension is that you burn carbohydrates, which don't have much to spare, then start burning down your protein, reducing your muscle mass. Your entire respiratory system is compromised by low oxygen tension. Your appetite is reduced because you are under severe physiological stress.

The sherpas in the Himalayas eat a very high fat diet. They don't read the literature about carbo. loading, and they survive much better than the climbers on the high carbo. diets Fat is fuel, the high test variety.

Q: One component of fat that gets much public attention is cholesterol. Yet there seems to be some debate as to whether reducing your cholesterol makes any difference, except in people with genetic hypercholesterolemia. How does cholesterol fit into the diet?

A: It is true that people with high serum cholesterol have a higher risk of heart disease. Two kinds of people have high serum cholesterol. One kind has lousy genes that can't control cholesterol synthesis. These people need to be treated with drugs that lower endogenous cholesterol levels. They also need to reduce weight. Similar pathways are involved in making and storing lipids and making and storing cholesterol. People on TPN have zero cholesterol in their bags. They make all of their own cholesterol. The whole idea that dietary is the causal link to high serum cholesterol is wrong. What is right is- show me a high cholesterol food and I'll show you a high fat food. You go for seconds and you're not working out, you've got problems.

Q: And yet talk to anyone on the bus and they think lowering cholesterol is a good idea.

A: Right, because it says so on television. The doctor and scientist types appearing on television are telling people that cholesterol in the diet is a fundamental issue. It is not. It is only an indirect issue.

Q: The Mediterranean diet appears to contain the basic elements of a well balanced, low fat diet. Can we learn about nutrition by looking at the cultural phenomenon of food?

A: The ideal Mediterranean diet contains the TPN nutrients in the form of the old basic four food groups. The key to diets like the Mediterranean diet is the cultural attitude that you don't eat a lot of it. It came about originally for economic reasons but the attitude persists for moderate consumption. In some poor areas they couldn't have rich foods. Gluttony is not part of those cultures.

Look at the Japanese situation. Their native diet is very low fat, but with an increase in Western fatty foods, we see an increase in heart disease and obesity. The most nutrient dense food in the supermarket containing all 44 nutrients and all four food groups is a pizza. So its crazy to call pizza junk food. Similarly, why call an apple a health food? What does it contain? Very little in the way of nutrients. It comes down to the same thing again, a balance of calories and nutrients determined by your age, sex, and your lifestyle.

Q: Part of the Mediterranean diet is a nice glass of wine. Is there enough data now to conclude benefits from alcohol in the diet?

A: Basically, it appears that alcohol is good for you in limited amounts, currently defined as between one and three drinks per day. The evidence from prospective and retrospective randomized studies is unambiguous. The evidence shows that moderate alcohol consumption reduces the incidence of coronary heart disease. It doesn't have to be wine and it doesn't have to be red. The issue is alcohol. Alcohol acts to reduce the time of blood clotting and thus prevent clot formation in the vessels leading to the heart. Alcohol also shifts the concentration of lipid density in favor of HDL. Moreover, a couple of glasses of wine can reduce a lot of psychological stress that can lead to hypertension. The bad news is that some people can't handle one or two drinks. Alcoholism is a serious disease. Again, this comes down to individual awareness and decision making.

Related information on the Internet

AE/UCSD Online Nutrition Course

Classroom Activity

Nutrition Resources

Lifelines

Worldguide Health & Fitness Forum

Dr. Art Ulene

USDA Nutrition Info.