Meatless diets and immunity

Immunity is on everyone’s mind these days. Immune function depends on nutrients. Some nutrients have a bigger impact on immune function than others. Zinc and vitamin D are two examples. Because of diet restrictions, vegetarians and vegans can have a harder time consuming sufficient amounts of some key immunity nutrients.

Immunity Basics

A healthy immune system responds to an invasive pathogen in 3 general ways:

  1. Physical and chemical barriers can keep the pathogen out of your system. Skin, mucous membranes and the little hairs in your nose are examples of physical barriers that can trap and exclude pathogens. Examples of chemical barriers include saliva, the gastric acid in your stomach and enzymes in tears.
  2. If a virus or bacteria gets past the barriers, the first response is innate immunity, which includes white blood cells, inflammation and fever.
  3. When a specific invasive pathogen is identified, acquired immunity kicks in. Your immune system creates a sort of memory of the virus so that killer cells can recognize and attack it.

Nutrients of concern for vegans and vegetarians

Vegetarians don’t eat meat, while vegans avoid all foods sourced from animals. Unfortunately those foods are our best sources of some key immunity nutrients:

Zinc

Zinc is critically important for all aspects of immune function, from skin integrity to immune cell activity. Zinc is not stored in the body, so daily intake is important. Meat and fish (particularly oysters) are the most concentrated sources of easily absorbed zinc. Vegetarians can get some from milk, cheese, yogurt and eggs. Vegans are limited to nuts, beans and whole grains as zinc sources.

On paper, those sources look fine, as long as you eat sufficient amounts everyday. The problem is absorption. Plant foods contain fibers that can interfere with zinc absorption. So you might think you’re eating sufficient amounts, but if you aren’t absorbing it, it’s not helping you. Some zinc experts believe vegans should consume up to 50% more zinc to make up for absorption problems due to plant fibers.

Foodamountzinc mg
Egg1 whole1.3
Milk, 2%8 oz1.0
Cheese (cheddar)1 oz1.0
almonds1/4 cup1.1
pinto beans, drained1 cup1.6
whole wheat bread1 slice0.6
peanut butter1 tablespoon0.4
ground beef, cooked4 oz6.8

An 18 year old female needs 9 mg of zinc daily. If she follows a vegan diet, she should consume about 14 mg/day from food. Young children who are vegan or even vegetarian might struggle to consume enough food volume to meet higher zinc intake recommendations.

Absorption and food volume aren’t the only concerns. Newly minted vegetarians and vegans think these diets are all about highly processed fake “alternative” meat and dairy foods. These products may not contain equivalent amounts of zinc. For example, almond milk has a mere 0.1 mg zinc, compared to cow’s milk with ten times as much.

Vitamin D

Vitamin D is naturally present in few foods; egg yolk is one example. D is added to some foods. Milk is fortified with vitamin D. Many processed foods contain added vitamin D. Examples include plant-based alternative “milks”, ready-to-eat cereals, snack bars and some juices. Our sample 18 year old girl needs 600 IU (15 micrograms) of D daily. She’d need to drink the equivalent of 6 cups of milk to achieve that intake.

Note that vitamin D is a concern for everyone, not just vegans and vegetarians. The problem for vegetarians/vegans is that many don’t consume fortified foods in significant quantities and can end up with insufficient vitamin D intake.

Omega-3 fatty acids

Omega-3 fats have unique roles to play in immune function. They are metabolized to inflammatory modulators. Unfortunately, there is no official daily recommended intake yet. Food sources of the most potent omega-3 fats are limited to fatty fish like salmon. Some plant foods contain the less biologically active omega-3 alpha-linolenic acid (ALA). Vegans and vegetarians can consume ALA from canola oil, flax seed and walnuts. Some foods — breads or cereals — are fortified with small amounts of omega-3.

Good News Nutrients

Vegetarian and vegans diets are likely to be good sources of other key immune nutrients: vitamin A, vitamin C, vitamin E and plant phenols. Plus vegetarian and vegan diets would encourage a healthy gut microbe population, thanks to all those plant foods. This is important because much of our immune function originates in the gut.

On the other hand: Beware the Anti-Vegetable Vegetarian. If this sounds silly, it’s not. Teenagers are especially likely to adopt meatless diets that emphasize processed foods, with few fresh whole foods like vegetables or whole grains. That sort of diet is just as bad for immune function as a garden-variety burger-and-fries diet. Intake of these other key immune nutrients will be poor.

What should you do?

Vegetarians:

  • Consume plenty of high zinc foods everyday: dairy foods, eggs, legumes, nuts/seeds/nut butters and whole grains. Keep in mind, the fibers in whole grains interfere with zinc absorption.
  • Fortified dairy foods will provide some vitamin D. Other fortified foods can help as well: ready-to-eat cereals, energy bars. If you are low on vitamin D, a supplement may be advisable.
  • Be sure to include plenty of vegetables and fruits in your daily diet to ensure good intake of other immunity nutrients.

Vegans

  • Include plenty of higher zinc foods in your diet every day. Stick to whole foods rather than processed foods: legumes (beans), nuts/seeds/nut butters, whole grains. Whole grain foods that are fermented (sourdough breads, yeast bread, sprouted grains) are less likely to inhibit absorption.
  • Find vitamin D fortified foods. Many plant “milks” are fortified, as well as some cereals. If you have significant sun exposure, you may be fine, but this depends on your use of sunscreen, where you live and time of year. A simple blood test can tell if you are insufficient in D.
  • Include ALA food sources like flax, canola oil, chia and walnuts in your diet, preferably some of these everyday. Omega-3 fortified foods rarely provide much omega-3, so don’t rely on those. Frequently just one omega-3 fat is added: DHA, which is synthesized using algae. If you don’t use those higher ALA foods often, you might consider a supplement.

Supplements

If you decide on to supplement any of these immune system nutrients, you can find many engineered for vegetarians and vegans. Examples include algae-derived omega-3 and vitamin D2 (not D3). If your diet is loaded with legumes, nuts, whole grains, vegetables and fruit, your intake of these nutrients might be fine. Problems are most likely for people who avoid entire food groups, or who rely heavily on the more processed vegan foods.

You can find lots of more detailed information about supplementing vegan and vegetarian diets in “Feed Your Vegetarian Teen 2nd Edition”.

Copyright: All content © 2021 Nutrition Strategy Advisors LLC. Photographs © Donna P Feldman, unless otherwise attributed. Reproduction or use without permission is prohibited.