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What is a plant-based diet and why should you try it?

November 16, 2021

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photo of Katherine D. McManus, MS, RD, LDN

Katherine D. McManus, MS, RD, LDN, Contributor

Kathy McManus is Director of the Department of Nutrition and Director of the Dietetic Internship at the Brigham and Women’s Hospital, a teaching affiliate of Harvard Medical School in Boston. In addition, she serves as the … See Full Bio
View all posts by Katherine D. McManus, MS, RD, LDN


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November 20, 2018


November 3, 2018

We would like to eat a more plant based diet but find the protein & carb issue confusing. My husband is diabetic so I first choose a protein (usually lean chicken, fish or beef). Then I choose low carb vegies and then some small amount of carb., if he eats too much carb his blood sugar goes up, especially if he hasn’t had protein. If he has eggs at breakfast he’s fine, if he has oatmeal with no protein his blood sugar goes up. If beans & grains are the protein on a plant based diet, they’re also high carbs. How can this work for a diabetic? Also, to me, the word ‘protein’ has always meant some kind of meat, cheese or eggs and the proper portions for a protein I understand. I have a hard time thinking of beans & grains as protein and how they are equivalent to meat, eggs & cheese. To me they are a carb and I worry that he won’t get enough protein. Any suggestions?

Kathy McManus
November 6, 2018

To help your husband control his blood glucose he can continue to consume small amounts of fish, chicken and eggs with his meals. Beans and grains are plant proteins, but do contain carbohydrate. Most animal based proteins contain more protein and only a very small amount of carbohydrate. Healthy eating patterns are not a one size fits all. Individuals should choose foods that work best for them and support decreasing their health risks.

Nancy .
October 26, 2018

Always good to examine various sides of an issue. Towards the beginning of this article it’s mentioned that our body’s cells prefer glucose for energy, which only comes from carbohydrates. The only animal product with any carbs is dairy. At some point in human evolution we must realize that adults have no need for breast milk after infancy,, especially the milk of another species. There are mountains of the most reliable scientific research that supports the superior health benefits of a whole-food, 100% plant-sourced diet. A good deal of this is found at the NutritionFacts website, which is a .org site. Another crucial issue which we cannot afford to ignore, if we want the human race to survive, is the devastating impact of all animal agriculture (including fowl and fish) on the environment and resource usage. Many reliable resources are easy to,find online, among them includes a site with information collected from various sources:

October 21, 2018

Think that it is not enough to eat healthy foods, but to add herbs and to check that the food that is eaten is as organic as possible, and that there are no unnecessary spraying or raise some of your food in your garden or on your balcony.
Recently I investigated the subject and came to an interesting book The Lost Book of Remedies, how to find them and how to grow on your own.

October 15, 2018

Dr. T Colin Campbell coined the term “whole food, plant based diet” and he did define it as meaning only plant based foods and no animal products so I think the author incorrectly defines the term “plant based” which is confusing. Plant based does mean vegan.

Lakdasa Dassanayaka
October 7, 2018

I have one question to ask you

Tomatoes are very easy to prepare. You don’t have to cook them, you can eat it as a salad , raw…..But easy things have adverse side effects. Does tomatoes cause kidney stones?

Please reply.


Kathy McManus
October 8, 2018

There is no research to support that tomatoes cause kidney stones – so enjoy them

Lakdasa Dassanayake
October 5, 2018

Your dietary advise was very valuable. I am only a vegetarian ( I thought vegan and vegetarian meant the same) . I think people eat meat more for its taste than for its nutrition. Unfortunately taste and nutrition seem to be going in opposite directions. I became a diabetic before becoming a vegetarian .I also have a bit of cholesterol. I have been able to reduce same by frequently taking green tea, roasted peanuts and olive oil. I have the following questions to ask you?

1) Your article mentioned barley. Does barley give the same amount of carbohydrates /energy/nutrition as Oates does for breakfast? can it replace Oates at least once a weak? 2) Your article also mentioned feta cheese. Is this the same as cottage cheese for people with cholesterol? 3) Doctors now say coconut milk is okay for cholesterol. I now take tea and even Oates with coconut milk. It tastes relay good and my cholesterol level has not gone up due to it either. Please answer the above.


Kathy McManus
October 5, 2018

Barley and oats are both whole grains. The nutritional content is somewhat different. Comparing 2 oz. raw : barley is higher in total carbohydrate (44 g) vs. oats (38 g) ; higher in fiber (9 g) vs. (6g) , but lower in protein (6 g) vs. (10 g). Both are low in saturated fat, sodium and sugar. Barley can be used as a replacement for oats.
Comparing feta cheese with low fat (1%) cottage cheese: (~ 1/4 cup) feta cheese is significantly higher in saturated fat (5 g) vs. (1g) so when looking for heart healthy food choices to help reduce LDL cholesterol – low fat cottage cheese has the edge. However – feta cheese does not need to be avoided – it has a wonderful taste and can be used in moderation.
Coconut milk is high in saturated fat and therefore a low fat milk is a better choice to use on a daily basis. However, for special occasions – using coconut milk in recipes that traditionally call for its inclusion is fine.

October 2, 2018

Harvard’s healthy eating is the most reliable. I sincerely follow the suggestions for a better health. Apart from the Mediterranean diet
Could you please tell us about the Nordic diet as well. Thank you for your admirable service to the community

Kathy McManus
October 3, 2018

The Nordic diet is similar to the Mediterranean eating pattern in that it is plant based. The diet includes whole grains, berries and other fruits, vegetables, legumes and fish, especially fatty fish such as herring, salmon and mackerel. Both diets include some eggs and dairy, but limit red meat, processed foods and sweets. See blog below for more details.

Rafael Pelegrina Pieroni
October 2, 2018

Could you please comment, maybe in a future post, a bit about on the epidemiological meta-analyses that show how animal protein can really affect human health even in small amount? Great post. Thanks for sharing your expertise.

Don Bougher
October 1, 2018

Regarding the first paragraph…
I thought beans were legumes. Your posting says….”legumes and beans.” ???

Kathy McManus
October 3, 2018

Sorry for the confusion. Legumes are a class of vegetables that includes beans, peas and lentils.

Dawn Cooper
October 1, 2018

Is this like the Zane method whitch I underdatand you approve?

October 1, 2018

This flexible, plant based approach to diet makes it easy to eat in restaurants and for family members that may not share your diet ideas to dine with you. I especially like the flexitarian diet. Above all, I personally avoid refined sugar and flour, but never explain to others why because either they will feel bad or not understand anyway. Instead, Just joke about it, like, never on Mondays.

joseph novakovich
October 1, 2018

I am surprised that you offer so many grilled menus, when grilling has been associated with cancer acceleration. You can eat plant based dishes without charcoal.

Clifton Rothman, M.D.
October 1, 2018

As a retired physician I can not determine which grains are whole grains because of labeling of breads etc. Multigrain, whole wheat, but other grains are listed etc. Help me.

Kathy McManus
October 3, 2018

In reviewing bread labels – look for breads that have “whole” as the first ingredient. I also suggest that consumers choose breads that have only a few ingredients and are without additives and sugar.

Dr David Drake, PhD
October 1, 2018

I’d caution readers to view the claims that olive oil is “heart healthy” with a bit of scepticism. Ask the question of “healthy compared to what”. That said, I’m really pleased that Harvard is showing that a plant-based diet leads to healthy long term outcomes. I’d add that if you want to lose weight fast, go vegan, exercise, and avoid sugary snacks. I lost 40 pounds in one year by ditching dairy products. Now 75 years old, I can hike any rugged trail I want. Before losing the excess weight, I found hiking mountains to be very challenging.

Betty Anne winstone
October 1, 2018

This is one of the most important and informative blogs I have received from Harvard. Thank you!

October 1, 2018

Great information; thank you!

Tom David
October 1, 2018

Just interested in your thoughts about milk, I try to have about a cup a day, drink more water than anything else, no coffee, tea on occasion and like sparkling water that comes from machine that I put CO2 cartridges in. Occasional diet cola from can or in restaurant for convenience mostly.

Kathy McManus
October 3, 2018

A cup of milk a day is reasonable. I would recommend low fat since it is lower in saturated fat than whole milk. Diets high in saturated fat can increased LDL cholesterol, a risk for cardiovascular disease.

September 30, 2018

Having a problem with your plant-based meal examples. The following are NOT plants: scrambled eggs, Monterey jack cheese, feta cheese, olive oil, mozzarella cheese, and more oil.

True plant-based diets have no dairy, no meat or eggs, and no oil. All of these things cause stiffening of the arteries and lead to heart disease, including the olive oil. Eggs (which are meat) and dairy encourage cancer growth and other diseases.

The rest of the meals are nice ideas, but meat and dairy in moderation cause disease in moderation.

Dr. J C Garcia-Alonso
October 3, 2018

I think you have a misconception or two. Oil do come from plants, canola, olives, sunflowers and avocados. Second oils are needed to absorb some vitamines like A, D, E and K.
On the other hand, moderate organic (here the key) dairy consumption have been proven beneficial in muscle building, lowering blood pressure and low-density lipoprotein cholesterol and preventing tooth decay, diabetes, cancer, and obesity.
Now take all this milk full of antibiotics and hormones to keep the cow producing, add preservative to make it long lasting milk and on top add a couple of spoons of sugar, and you will have all the previous mention diseases. Similar with eggs and cheeses.

Kathy McManus
October 3, 2018

Thanks for your comment. The blog was aimed at directing consumers toward a more plant based diet – not exclusively vegan. There is much research to support the reduced risk of chronic disease with healthy dietary patterns such as the Mediterranean Diet and DASH (Diet Approaches to Stop Hypertension) that are predominately plant based, but do include some animal products.

Commenting has been closed for this post.

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