Nutrition in Clinical Medicine

In 1957, a surgeon named Denis Burkitt first encountered a puzzling form of childhood cancer. The condition, which came to be called Burkitt’s lymphoma, caused a massive swelling of the jaw and was often fatal. But Burkitt noticed something peculiar: The disease followed a geographic pattern, never appearing far from the equator and the east coast of Africa. He painstakingly identified the cause—a virus (now known as Epstein-Barr) transmitted by an insect vector—and then found an effective treatment.[1] His lifesaving work was acclaimed throughout the world of medicine.

Soon thereafter, Dr. Burkitt set his sights on larger medical epidemics, whose solutions were hidden in a much bigger geographical puzzle. He noticed that the great bulk of diseases occurring in the Western world—heart disease, diabetes, obesity, and many others—were surprisingly rare in rural Africa. During 20 years of surgical practice throughout Africa, he removed only 2 gallbladders, something he might have done on a single morning in any London hospital. Many other conditions, from appendicitis to colon cancer, were rare in Africa, but common in Europe. He ruled out genetics as the main explanation, because people moving from one country to another eventually assumed the same risks as the populations in their adopted homes.

Burkitt proposed that the culprit was diet. In Europe and the Americas, diets bore no resemblance to a fiber-rich African diet. On the contrary, they were fiber-depleted and laden with fat, cholesterol, and sugar. His work, and that of other medical pioneers, launched a major rethinking of the fundamental causes of illness. Previously, nutrition had been thought to play a fairly minor role in health. Yes, there were rare deficiency states, such as pellagra or scurvy, but these were little more than details on medical school examinations. The major killer diseases were thought to have more to do with genes and bad luck than diet. But this new breed of researchers held that nutrition was decisive. It was a fundamental contributor to the major diseases that filled doctors’ waiting rooms throughout the Western world.

Burkitt proposed that health authorities should spend less time dealing with the results of bad diets and more time encouraging people to change the way they eat. To continue to treat illnesses while ignoring prevention, he said, was like a plumber mopping up a kitchen floor rather than turning off the tap in an overflowing sink. A new focus on nutrition and prevention could turn the tide in the chronic disease epidemics of our time.

Evolving Knowledge in Nutrition

Just as new medications often have advantages over previous ones, diet approaches evolve as well, with new dietary methods building on previous ones and research studies putting diets to the test. Heart-healthy diets are a case in point. For decades, cardiologists have encouraged heart patients to switch from red meat to white meat, trim away chicken skin, and stay physically active. These steps were modestly helpful. Following such guidance, an average patient experienced roughly a 5% drop in low density lipoprotein (LDL or “bad”) cholesterol.[2]

However, in 1990, a Harvard-trained physician named Dean Ornish published the results of a study using a much more vigorous regimen.[3] His research participants had significant heart disease. His experimental treatment included a very-low-fat, vegetarian diet, smoking cessation, modest exercise, and stress management. The diet was logical: Foods from plants have no cholesterol and no animal fat. For comparison, his study included a control group that received the usual care that doctors provide for heart patients.

The results made medical history. Not only did the program reduce cholesterol far more effectively than previous diets, but it visibly changed the disease process itself. Angiograms done before and after the 1-year intervention showed that participants in the control group gradually worsened. But the patients in the experimental group had a very different experience. Their coronary arteries were beginning to open up again, so much so that signs of reversal were clearly evident in 82% of participants within the first year.[3]

In 1999, Dr. Caldwell Esselstyn, a Cleveland Clinic surgeon, published the results of a remarkable 12-year study integrating nutrition with medications.[4] In a group of patients with severe heart disease, he used a diet similar to that used by Dr. Ornish. For any patient whose total cholesterol remained above 150 mg/dL despite the diet, he added cholesterol-lowering medications. In the ensuing 12 years, the research participants had no cardiac events. The combination of the diet and judiciously used medications made the patients practically heart-attack-proof.

Then, in 2005, David Jenkins, a researcher from the University of Toronto, took things a step further. He emphasized foods with known cholesterol-lowering properties—oats, soy, and certain nuts, for example. In four weeks’ time, LDL cholesterol fell nearly 30%.[5] As research has moved forward, our idea of an effective diet has advanced as well.

The same sort of trend has occurred in the approach to cancer. For many years, lifestyle advice from cancer authorities was limited to avoiding tobacco and getting regular checkups. But it has become clear that diet plays a major role in cancer risk. We now encourage all patients to include more fruits and vegetables in their routines; to focus on foods that are rich in antioxidants and fiber; and to limit or avoid red and processed meats, highly processed foods, and alcohol.[6]

More recently, nutritional steps have been tested not only for cancer prevention, but for cancer survival. Studies of individuals diagnosed with breast or prostate cancer have shown that diet may make a major difference in the ensuing years.

Safe and Effective

Dietary approaches are often remarkably effective. The cholesterol-lowering power of the diets used by Drs. Ornish, Esselstyn, and Jenkins rivals that of typical cholesterol-lowering medications. These diets’ effect on blood glucose control rivals that of oral diabetes drugs.[7] For migraines or arthritis, not everyone improves with dietary adjustments that eliminate common dietary triggers, but many do; in controlled clinical trials, sometimes simple diet changes bring dramatic improvements.

Unlike the undesirable side effects we associate with medications, healthful diet changes bring desirable side effects. People who adjust the menu in hopes of reducing their cholesterol get the bonus of losing unwanted weight. Their blood pressure drifts downward as well. If they have diabetes, it comes under better control, and they may be able to reduce their need for medication.

While many still think of medications as “conventional medicine” and dietary changes as “alternative therapies,” a growing number of clinicians would turn the definitions around. For many conditions, attention to diet and lifestyle is the foundation of good clinical care. Medications, surgery, or other treatments should be used when diet and lifestyle changes do not apply or are not, by themselves, sufficient for the task at hand.

Clinicians often come to find that problems they had once regarded as strictly medical, or perhaps even genetic—diabetes and cardiovascular disease, for example—have major nutritional antecedents. As time goes on, they start to see nutritional problems everywhere. The role of nutrition is indeed greater than most clinicians and patients realize. At the same time, not all problems have nutritional connections, and, even for nutrition-related conditions, medical diagnosis and treatment have as important a role now as ever.

The Nutrition Guide for Clinicians summarizes the most effective dietary interventions for common conditions and provides information to help patients and their families make healthful changes. A major trend in research, which is reflected here, is a renewed emphasis on plant-based diets. The diets now being offered to heart patients and the vegetable-and-fruit-rich diets advocated for reducing cancer risk are very different from the diets that are familiar to most patients and doctors. However, many doctors find these diets useful, and many patients will find them lifesaving. Readers will also find details on dietary factors that have adverse health consequences. There is no shortage of unhealthy foods in everyday life, and they exact a large and growing health toll. It is important to educate patients about these dietary risks.

How to Use This Resource

We suggest that readers consult the introductory topics devoted to basic nutrition topics and then look at chapters relevant to the conditions they see in practice. We also encourage a look at the supporting references.

Clinicians should not feel that they must be nutrition experts able to provide basic diet counseling. But just as clinicians need to know when to order an x-ray whether or not they know how the radiographic equipment works, they also need to know when a nutritional intervention is needed and how to refer patients appropriately to a registered dietitian nutritionist (RDN) for medical nutrition therapy.

This guide is updated regularly. It therefore goes without saying that no edition of the guide can be held to be the definitive work on nutrition. Science moves on, and we will continue to update as new information becomes available.

Each chapter was written by one or more physicians and a nutrition expert, and was reviewed by appropriate medical specialists. While the authors are pleased to present this clinical tool, we appreciate readers’ pointing out typographical errors and opportunities for improvement. Nutrition is as controversial as any other science—perhaps more so—and we welcome readers’ suggestions and criticisms. We also look forward to hearing from readers who would like to serve as reviewers for subsequent editions.

Finally, we should note that this work was originally intended to remedy the absence of clinically oriented nutrition information in the curricula of many medical schools. We hope readers will find ways to tackle the same problem. A new emphasis on prevention and nutrition in medical practice will be empowering for clinicians and potentially lifesaving for patients.


  1. Burkitt DP. The discovery of Burkitt's lymphoma. Cancer. 1983;51(10):1777-86.  [PMID:6299496]
  2. Hunninghake DB, Stein EA, Dujovne CA, et al. The efficacy of intensive dietary therapy alone or combined with lovastatin in outpatients with hypercholesterolemia. N Engl J Med. 1993;328(17):1213-9.  [PMID:8464431]
  3. Ornish D, Brown SE, Scherwitz LW, et al. Can lifestyle changes reverse coronary heart disease? The Lifestyle Heart Trial. Lancet. 1990;336(8708):129-33.  [PMID:1973470]
  4. Esselstyn CB. Updating a 12-year experience with arrest and reversal therapy for coronary heart disease (an overdue requiem for palliative cardiology). Am J Cardiol. 1999;84(3):339-41, A8.  [PMID:10496449]
  5. Jenkins DJ, Kendall CW, Marchie A, et al. Direct comparison of a dietary portfolio of cholesterol-lowering foods with a statin in hypercholesterolemic participants. Am J Clin Nutr. 2005;81(2):380-7.  [PMID:15699225]
  6. Rock CL, Thomson C, Gansler T, et al. American Cancer Society guideline for diet and physical activity for cancer prevention. CA Cancer J Clin. 2020;70(4):245-271.  [PMID:32515498]
  7. Barnard ND, Cohen J, Jenkins DJ, et al. A low-fat vegan diet improves glycemic control and cardiovascular risk factors in a randomized clinical trial in individuals with type 2 diabetes. Diabetes Care. 2006;29(8):1777-83.  [PMID:16873779]
Last updated: December 1, 2020