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Drawing on decades of professional experience, health psychologist Dr. Thomas Johnson reviews and critiques Harvard Medical School’s Food is Medicine, a guide to eating for disease prevention and optimal health that emphasizes whole food, plant-based dietary choices.

A Review of Harvard Medical School’s Food is Medicine
From Dr. Thomas Johnson, NCSP
June 2026

Images from Canva

Harvard Medical School’s Food is Medicine
Edited by Dr. Beth Frates, Associate Professor Physical Medicine & Rehabilitation & Meghan Ariagno, Registered Dietician Nutritionist
Review by Dr. Thomas Johnson, NCSP

“Let Food be thy medicine and let medicine be thy food” is a famous quote attributed to Hippocrates. This quote sets the stage for this informative and impressive publication. The authors offer the following as part of their introduction:

“As nutrition research has accumulated, so has a growing consensus that diet ought to play a larger role in society’s overall approach to health. This ‘food is medicine’ philosophy dovetails with a rising interest in lifestyle medicine and whole person health care. The goal is not simply to treat disease, but to target the root causes of chronic conditions and ideally prevent them before they arise” (p.1).

At the outset I think the readers of this paper should know that I have been a practicing health psychologist for several decades and have provided (along with my associates) lifestyle health care to thousands of patients/clients not only in the traditional areas of mental health and special education but also in any areas of health care in which stress control plays an important role—which, in my judgement, applies to most illnesses.

My interest in health, nutrition and exercise actually started in my teens when I was diagnosed with infectious hepatitis. Shortly after the diagnosis I was hospitalized and placed in quarantine. I became so ill that my weight dropped to 89 pounds and I became so weak that I could barely walk to the bathroom unaided. The medical literature indicate that this can be a life-threatening condition.

Fortunately, I survived and was able to live out the “silver lining” of my illness which resulted in motivation to eat healthy food including vegetables, fruit, legumes, whole grains and nuts. At the time of my illness animal protein was thought to be essential for health and muscle building; so, I ate a lot of tuna fish, cottage cheese, milk and other “animal products.” I had never heard the word vegetarian or of eating whole foods, plant-based meals. So that was not an option at the time. (The interested reader can read more about this in All-Creatures.org's April 2025 article, A Guide to Cognitive Fitness Part Three—based largely on the Harvard Medical School publication A Guide to Cognitive Fitness, edited by Dr. Alvaro Pascual-Leone.)

As part of my motivation to recover I took out my first magazine subscription which was to Strength and Health. At the time this was a highly regarded reference for athletes particularly in the weightlifting and bodybuilding communities. It was my primary source of guidance in the areas of nutrition and body building.

My strong motivation to increase my understanding of health and what decisions go into being healthy resulted in my accepting a Brown University Ph.D. U.S. Public Health Fellowship in social psychiatry and medical sociology. After this fellowship year I later moved on to additional graduate studies in counseling psychology/health psychology at Harvard University, UC-Berkeley and Duke University’s Counseling and Psychological Services Center. Currently this center is part of the Duke University School of Medicine.

Over the years after graduate school, I have also taken many post graduate CEU courses at the Harvard Medical School, The National Register of Health Service Providers in Psychology and the Institute for Natural Resources.

Additionally, I have also taught courses in psychopathology, educational psychology, general psychology, etc. to undergraduate students at Bates College. I have also taught graduate students in counselor education, counseling psychology and school psychology at the University of Southern Maine and Rutgers University.

In most of my post graduate roles I have had lifestyle health care and stress control in mind with a focus on the concept of food as medicine. Every patient coming into our psychological service center was offered the opportunity to receive a free copy of the Physicians Committee for Responsible Medicine publication handout on plant-based nutrition and health.

Nutritional medicine or lifestyle medicine were rarely referred to in my graduate studies. Also, in a recent review of doctoral programs in psychology I found few universities offering advanced training in lifestyle medicine/nutrition. One exception that I was able to locate was at Teachers College, Columbia University. Their program was listed as a Ph.D. in Behavioral Nutrition, but it appears to be primarily for those interested in research rather than direct clinical practice.

Lack of training in nutrition and health is reportedly the case in MD programs as well according to Dr. Michael Greger. In a recently released video on HOW NOT TO DIE (May 2026) he reports that even today comprehensive courses in nutrition are rarely offered in MD programs.

Given these realities in medicine and psychology graduate training, Food is Medicine could serve as an important publication for health care providers who lack the training in this area of health care as well as for patients.

The authors of this publication divide their writings into the following sections:

• Why Food is Medicine
• A Healthy Bounty of Foods
• Nutritional Prescriptions for Common Conditions
• Special Section: Applying the food-is-medicine approach to your life

In the first section—Why Food is Medicine—the authors discuss the macronutrients including proteins, carbohydrates and fats. They all provide the energy that fuels our bodies' functions, and all are essential in providing a healthy foundation for good health.

The authors also discuss the micronutrients including vitamins such as vitamins A, D, E, and K which are fat soluble. The water-soluble vitamins include vitamin C, choline, and the eight compounds known as B complex vitamins, calcium, potassium, phosphorus, iron, zinc, magnesium, selenium and iodine.

Perhaps one of the best takeaways from this section has to do with what foods cause or calm unhealthy inflammation. Foods that contribute to unhealthy chronic inflammation include red meat and processed meats which are high in saturated fats. These foods have been linked with increased risk of heart disease and cancer. Foods with added sugars like baked goods and sodas are foods that can also increase inflammation and cause weight gain.

The key to anti-inflammatory eating includes plant foods—whole grains, nuts, seeds, legumes, fruits and vegetables.

The second section of Food is Medicine is A Healthy Bounty of Foods.

This section focuses on the Healthy Eating Plate including vegetables, whole grains, fruits and healthy protein. Also included are water, tea and coffee. Alcohol is excluded because the recent research demonstrates that drinking alcohol on a regular basis even in so-called moderate amounts should be looked at as a risk factor for at least 7 types of cancer according to the Surgeon General.

Half of your plate should include vegetables and fruit. A quarter of your plate should include whole grains like brown rice, oats, corn, pasta and bread. A quarter of your plate should include beans, lentils, tofu and for non-vegetarians poultry and fish. The reader is cautioned not to eat processed meat and to limit red meat. Healthy plant oils which do not include hydrogenated oils are recommended.

The authors made some puzzling comments about fish. For example, on pages 14 and 15 they state, “Most Americans don’t eat much seafood, but many could benefit from getting a little more. US Dietary Guidelines recommend getting one to two servings of fish (about 6 to 8 ounces) per week.” They go on to describe the nutritional benefits of certain types of fish such as sardines, herring and salmon. Later on, they caution that “Toxic water pollutants such as polychlorinated biphenyls (PCBs) and mercury can accumulate in nearly all fish, especially larger ones like swordfish, tilefish, and king mackerel. For this reason, the FDA advises that children and people who are pregnant or breastfeeding should avoid these types of fish, and everyone else eat them only rarely” (p. 15).

While the authors wisely provide cautions about PCBs and mercury there is no mention of parasites in fish. The Physicians Committee for Responsible Medicine offers detailed documentation indicating that almost every fish sold in stores is infested with parasites. So, part of my puzzlement mentioned earlier is that the authors are promoting the health benefits of eating certain types of fish in moderation and at the same time offering cautions about the presence of mercury and PCBs in fish. There is no mention of the widespread presence of parasites in fish. The interested reader can go to the PCRM web site and look at the section referred to as the Exam Room. On the first page of this section of the web site the following is stated: “More than 90% of some wild-caught fish is estimated to be infected with at least parasite eggs, while more than 75% of filets from wild-caught salmon contain parasitic worms.” [Click here to listen to the episode of the Exam Room Podcast, You’re Eating Parasites If You're Eating Fish.]

As a result of these downsides of eating fish and because of ethical considerations, some of us are motivated to move on to totally plant based nutrition—also sometimes referred to as ethical vegetarianism or veganism.

To the authors’ credit, they do bring in ethical considerations as reflected in this passage: “Animal-based protein foods are an efficient way to get your protein, but it's important to prioritize healthier choices—as well as to consider their impact on our planet. Red meat and processed meats, for example, are important contributors of unhealthy saturated fat to our diets and require significantly more land and water resources to produce than other protein foods” (p.14). They then refer to another section of the publication under the title “healthier diet healthier planet.”

On page 26 the authors refer to climate change and a growing world population which “health researchers and environmental experts are converging on an understanding that the food we eat is as important to planetary health as it is to our dietary health.” Shifting to a more plant-based diet and reducing our intake of animal sourced foods, they argue, is a more sustainable use of our land and water resources. The EAT-Lancet Commission’s Planetary Health Diet developed by an international team of scientists, including some from the Harvard T.H. Chan School of Public Health, projects “that shifting to this way of eating (i.e. whole foods plant based) could prevent up to 11,000,000 premature deaths per year through improved heart health and lower risk of diet related diseases, as well as help lower greenhouse gas emissions and reduced deforestation” (p.36).

The third section is entitled Nutrition Prescriptions for Common Conditions and covers heart health, diabetes, cancer, understanding the glycemic index and glycemic load, gut health, bone health, kidney health, cognitive health and mental health.

With respect to all of these conditions the authors explain that treating chronic diseases is not just about taking prescription medicine but also means practicing lifestyle changes like exercising more, eating more plant-based meals, getting restorative sleep, stress management and mental health support.

As a health psychologist this is consistent with how I try to provide guidance for my patients/clients and how I encourage my consultees and students as they develop their professional identities.

The two areas I will comment on include cognitive health and mental health as they are the primary areas of my training and practice.

Cognitive health “refers to those mental functions essential to the daily activities of living, such as making decisions, solving problems and communicating effectively” (p.35).

The authors recommend “key eating strategies for preventing dementia including the following:
Focus on vegetables daily
Get at least three servings of whole grains daily
Eat at least two servings of berries per week
Choose healthy proteins” (p. 35).

As with cognitive health the authors point out that

“emerging research suggests diet can play an important role in helping manage depression and anxiety symptoms… In general, a diet supportive of mental health is a primarily plant-forward one that includes ample amounts of vegetables, fruits, whole grains, and healthy fats while limiting meat, processed foods, and added sugars.

A Mediterranean type eating pattern has been linked with lower rates of depression and anxiety in several studies. Adding more foods that support a healthy microbiome—the populations of good bacteria that live in the gut—can also help” (p. 36).

The Mediterranean diet is referred to many times in this publication, and its value in treating depression has been discussed in multiple publications, including this one. Up until recently the specific food that decreases depression had not been identified and it is not identified here. However, recently I read in my Harvard Alumni Magazine July/August 2025 issue that it is the citrus in the diet that has the antidepression effect. The title of the article is “Can an Orange a Day Stave off Depression?” by Erin O’Donnell.

Again, we have evidence that indicates the importance of health care practitioners being up to date on the importance of dietary health in treating mental health problems—ideally without having to resort to drugs that only treat symptoms. Only using drugs to treat symptoms may distract practitioners and patients alike from what may be missing in a person’s diet and other lifestyle practices like exercise and restorative sleep.

The last section in this publication is Applying the food-is-medicine approach to your life.

This section can be summed up with the following quote:

“With the busy lives we all lead, taking the time to plan, shop, and prepare food can feel like a lot—but it's worth the effort. By being more intentional in your actions, you'll have better control over the foods you eat daily and how you eat them. That can pay off in big dividends for your health and happiness” (p.38).

The publication ends with 4 recipes including the following:

• Veggie Meal for Meat Lovers – Chipotle black bean quinoa veggie burgers
• Easy to freeze - Kabocha Squash and Leek Soup with Pistachios
• Easier than cookout – Mandarin Orange Quinoa and Kale Bowl
• Budget friendly – Chickpea Masala with Brown Rice

See pages 39-42 for the details.

In summary and conclusion, this Harvard Medical School publication Food is Medicine provides generally up to date knowledge to health care practitioners and patients. As referenced in this article, training in doctoral programs in medicine and psychology tends to be limited, so I see this Harvard Medical School publication as providing an excellent introduction to providers and patients alike. Ideally, as practitioners and patients appreciate the many benefits that can come from implementing the knowledge in this publication, they will also realize that ongoing research—like the recent studies on the benefit of citrus in improving health and especially mood levels—they will realize the importance of trying to stay up to date on studies that demonstrate health benefits.

The one area that I would like to see updated has to do with whether or not fish should be viewed as a health food. Dr. Neal Barnard and other PCRM medical practitioners and scientists argue that fish should not be viewed as a health food because of the widespread presence of PCBs, parasites and mercury. Again, this illustrates the importance of staying up to date on important knowledge from nutrition, lifestyle medicine and health.

Learn more about Dr. Thomas Johnson and see his other contributions to All-Creatures here!

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Posted on All-Creatures: June 7, 2025
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We began this archive as a means of assisting our visitors in answering many of their health and diet questions, and in encouraging them to take a proactive part in their own health. We believe the articles and information contained herein are true, but are not presenting them as advice. We, personally, have found that a whole food vegan diet has helped our own health, and simply wish to share with others the things we have found. Each of us must make our own decisions, for it's our own body. If you have a health problem, see your own physician.