Plant-Based or Animal-Based Diet: Which Is Better?

Akshay B. Jain, MD; Christopher Gardner, PhD , July 28, 2023. Akshay B. Jain, MD: Hello. Thanks for joining us. I’m Akshay Jain, an endocrinologist in Vancouver, British Columbia. Joining us is Dr Christopher Gardner, a nutritional scientist at Stanford. He is the author of many publications, including the widely cited SWAP-MEAT study. He was also a presenter at the American Diabetes Association conference in San Diego in 2023.We’ll be talking about his work and the presentation that he did classifying different kinds of diets as well as the pluses and minuses of a plant-based diet vs an animal-based diet. Welcome, Dr Gardner.

Christopher Gardner, PhD: Glad to be here.

Jain: Let’s get right into this. There’s obviously been a large amount of talk, both in the lay media and in the scientific literature, on plant-based diets vs animal-based diets. When it comes to an individual living with diabetes, does one diet make more sense than the other?

Gardner: I think this is one of those false dichotomies. It’s really not all one or all the other. Two of my favorite sayings are “with what” and “instead of what.” You may be thinking, I’m really going to go for animal-based. I know it’s low-carb. I have diabetes. I know animal foods have few carbs in them.

That’s true. But think of some of the more and the less healthy animal foods. Yogurt is a great choice for an animal food. Fish is a great choice for an animal food with omega-3s. Chicken McNuggets, not so much.

Then, you switch to the plant side and say, “I’ve heard all these people talking about a whole-food, plant-based diet. That sounds great. I’m thinking broccoli and chickpeas.”

I know there’s somebody out there saying, “I just had a Coke. Isn’t that plant-based? I just had a pastry. Isn’t that full of plants?” It doesn’t really take much to think about this, but it’s not as dichotomous as animal vs plant.

Jain: There is, obviously, a good understanding regarding what actually constitutes the diet. Initially, people were saying that animal-based diets are really bad from a cardiovascular perspective. But now, some studies are suggesting that it may not be true. What’s your take on that?

Gardner: Again, if you think “with what” or “instead of what,” microbiome is a super-hot topic. That’s really fiber and fermented food, which are only plants. Saturated fat, despite all the controversy, raises your blood cholesterol. It’s more prevalent in animal foods than in plant foods.

Are there any great nutrients in animal foods? Sure. There’s calcium in dairy products for osteoporosis. There’s iron. Actually, people can get too much iron, which can be a pro-oxidant in levels that are too high.

The American Heart Disease, in particular, which I’m very involved with, came out with new guidelines in 2021. It was very plant-focused. The top of the list was vegetables, fruits, whole grains, and protein. When it came to protein, it was mostly from lentils, beans, and grains.

Jain: That’s good to know. Let’s talk about protein. We often hear about how somebody on a plant-based diet only can never have all the essential amino acids and the amount of protein that one needs. Whether it’s for general everyday individuals or even more so for athletes or bodybuilders, you cannot get enough good-quality protein from a plant-based diet.

Is there any truth to that? If not, what would you suggest for everyday individuals on a plant-based diet?

Gardner: This one drives me nuts. Please stop obsessing about protein. This isn’t a very scientific answer, but go watch the documentary Game Changers, which is all about vegan athletes. There are some pretty hokey things in that film that are very unscientific.

Let’s go back to basics, since we only have a couple of minutes together. It is a myth that plants don’t have all the amino acids, including all nine essential amino acids. I have several YouTube rants about this if anybody wants to search “Gardner Stanford protein.” All plant foods have all nine essential amino acids and all 20 amino acids.

There is a modest difference. Grains tend to be a little low in lysine, and beans tend to be a little low in methionine. Part of this has to do with how much of a difference is a little low. If you go to protein requirements that were written up in 2005 by the Institute of Medicine, you’ll see that the estimated average requirement for adults is 0.66 g/kg of body weight.

If we recommended the estimated average requirement for everyone, and everyone got it, by definition, half the population would be deficient. We have recommended daily allowances. The recommended daily allowances include two standard deviations above the estimated average requirement. Why would we do that? It’s a population approach.

If that’s the goal and everybody got it, you’d actually still have the tail of the normal distribution that would be deficient, which would be about 2.5%. The flip side of that argument is how many would exceed their requirement? That’s 97.5% of the population who would exceed their requirement if they got the recommended daily allowance.

The recommended daily allowance translates to about 45 g of protein per day for women and about 55 g of protein per day for men. Today, Men and women in the United States get 80 g, 90 g, and 100 g of protein per day. What I hear them say is, “I’m not sure if I need the recommended daily allowance. I feel like I’m extra special or I’m above the curve and I want to make sure I’m getting enough.”

The recommended daily allowance already has a safety buffer in it. It was designed that way.

Let’s flip to athletes just for a second. Athletes want to be more muscular and make sure they’re supporting their activity. Americans get 1.2-1.5 g of protein per kg of body weight per day, which is almost double.

Athletes don’t eat as many calories as the average American does. If they’re working out to be muscular, they’re not eating 2000 or 2500 calories per day. I have a Rose Bowl football player teaching assistant from a Human Nutrition class at Stanford. He logged what he was eating for his football workouts. He was eating 5000 calories per day. He was getting 250 g of protein per day, without any supplements or shakes.

I really do think this whole protein thing is a myth. As long as you get a reasonable amount of variety in your diet, there is no problem meeting your protein needs. Vegetarians? Absolutely no problem because they’re getting dairy and some eggs and things. Even vegans are likely fine. They would have to pay a little more attention to this, but I know many very strong, healthy vegans.

Jain: This is so helpful, Dr Gardner. I know that many clinicians, including myself, will find this very helpful, including when we talk to our patients and counsel them on their requirements. Thanks for sharing that.

Final question for you. We know people who are on either side of the extreme: either completely plant-based or completely animal-based. For a majority of us that have some kind of a happy medium, what would your suggestions be as far as the macronutrient distribution that you would recommend from a mixed animal- and plant-based diet? What would be the ideal recommendations here?

Gardner: We did a huge weight loss study with people with prediabetes. It was as low in carbs as people could go and as low in fat as people could go. That didn’t end up being the ketogenic level or the low-fat, vegan level. That ended up being much more moderate.

We found that people were successful either on low-carb or low-fat. Interestingly, on both diets, protein was very similar. Let’s not get into that since we just did a lot of protein. The key was a healthy low-carb or a healthy low-fat. I actually think we have a lot of wiggle room there. Let me build on what you said just a moment ago.

I really don’t think you need to be vegan to be healthy. We prefer the term whole-food, plant-based. If you’re getting 70% or 80% of your food from plants, you’re fine. If you really want to get the last 5%, 10%, or 15% all from plants, the additional benefit is not going to be large. You might want to do that for the environment or animal rights and welfare, but from a health perspective, a whole-food, plant-based diet leaves room for some yogurt, fish, and maybe some eggs for breakfast instead of those silly high-carb breakfasts that most Americans eat.

I will say that animal foods have no fiber. Given what a hot topic the microbiome is these days, the higher and higher you get in animal food, it’s going to be really hard to get antioxidants, most of which are in plants, and very hard to get enough fiber, which is good for the microbiome.

That’s why I tend to follow along the lines of a whole-food, plant-based diet that leaves some room for meat and animal-sourced foods, which you could leave out and be fine. I wouldn’t go in the opposite direction to the all-animal side.

Jain: That was awesome. Thank you so much, Dr Gardner. Final pearl of wisdom here. When clinicians like us see patients with diabetes, what should be the final take-home message that we can counsel our patients about?

Gardner: That’s a great question. I don’t think it’s really so much animal or plants; it’s actually type of carbohydrate. There’s a great paper out of JAMA in 2019 or 2020 by Shan and colleagues. They looked at the proportion of calories from proteins, carbs, and fats over about 20 years, and they looked at the subtypes.

Very interestingly, protein from animal foods is about 10% of calories; from plants, about 5%; mono-, poly-, and saturated fats are all about 10% of calories; and high-quality carbohydrates are about 10% of calories. What’s left is 40% of calories from crappy carbohydrates. We eat so many calories from added sugars and refined grains, and those are plant-based. Added sugars and refined grains are plant-based.

In terms of a lower-carbohydrate diet, there is an immense amount of room for cutting back on that 40%. What would you do with that? Would you eat more animal food? Would you eat more plant food? This is where I think we have a large amount of wiggle room. If the patients could get rid of all or most of that 40%, they could pick some eggs, yogurt, fish, and some high-fat foods. They could pick avocados, nuts, seeds, and olive oil or they could have more broccoli, chickpeas, tempeh, and tofu.

There really is a large amount of wiggle room. The key — can we please get rid of the elephant in the room, which is plant food — is all that added sugar and refined grain.

Jain: That was brilliant. Thank you so much, Dr Gardner, for joining us today.

This is Akshay Jain, signing off for Medscape.

Gardner: It’s been a pleasure, Akshay. Thanks.