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Back to Table of Contents | December 2012

Clinical and Health Affairs

Nutritional Assessment in Vegetarians and Vegans

Questions Clinicians Should Ask

By Gregory A. Plotnikoff, M.D., M.T.S., FACP

■ Not all who adhere to vegetarian, vegan or other special diets have nutritionally sound eating habits. The clinical consequences of an insufficiently mindful vegetarian or vegan diet include many common symptoms such as anxiety, brain fog, depression, fatigue, insomnia, neuropathies and other neurologic dysfunction. Patients with such symptoms who report having a vegetarian or vegan diet, or a diet that severely restricts meat consumption, require a slightly expanded differential diagnosis. The challenge is to identify which patients require closer attention. This article lists questions to use to quickly assess for potential dietary drivers of clinical symptoms. In many cases, simple nutritional interventions, through diet and/or supplementation, can resolve or minimize problematic symptoms.


A vegetarian diet or even a vegan diet (one that excludes all meat, poultry, fish, eggs and dairy products) can be a very healthy choice. However, eating a nutritionally sound vegetarian or vegan diet requires knowledge, motivation and discipline. It also requires advance planning, as healthy and well-balanced options for vegetarians and vegans are rarely available in cafeterias and restaurants. Not everyone who professes to have a meat-free diet follows healthy eating patterns. Additionally, too many people confuse eating a meat-free diet with eating a healthful vegetarian diet. They might see a diet rich in cheese as adequate, for example. It is not. Simply eliminating meat from one’s meals is not enough. And doing so can place one at high risk for clinically significant nutritional insufficiencies.

The clinical consequences of an insufficiently mindful vegetarian or vegan diet include common symptoms such as anxiety, brain fog, depression, fatigue, insomnia, neuropathies and other neurologic dysfunction. Patients with such symptoms who report having a vegetarian or vegan diet, or a diet that severely restricts meat consumption, require a slightly expanded differential diagnosis. In many cases, simple interventions can resolve or minimize their symptoms. Even for vegetarians and vegans who pay close attention to diet, three supplements are commonly required: vitamin B12, amino acids and DHA. The clinician’s challenge is to identify which patients require closer attention. This article seeks to provide a quick guide for assessment in the clinical setting.

The First Step
Clinicians are often prompted by their electronic medical record to note whether a patient has any history of special diets including vegan, vegetarian, kosher, hallal or other traditional diets. This is actually helpful. For example, a question about a special diet may lead to discussion about a previous or current eating disorder.

Perhaps more importantly, however, inquiries about a patient’s dietary preferences can lead to dialogue about his or her religious, spiritual and ethical beliefs. “Tell me about it” and “Tell me about why this is important to you—what would you most want me to know?” are questions that will elicit the meanings, beliefs and interpretations that inform the patient’s values and evoke details that can be important to clinical decision making. A patient’s answers may reveal factors behind apparent resistance to or noncompliance with clinical advice. For example, some patients may resist taking pills, capsules and gel capsules if they perceive animal products are used in their manufacture.

Questions to Ask Vegetarians and Vegans
Optimal clinical practice involves asking patients how they define “vegetarian” and “vegan” and what they actually eat. Assessment of key nutritional knowledge is also medically appropriate. The following questions can help you uncover information that will be helpful for clinical reasoning. A patient’s inability to answer any of these is a red flag for potential dietary insufficiencies. (The questions get progressively more difficult to answer.)

■ Q: What is a complete protein?
A: Complete protein intake includes all of the essential and conditionally essential amino acids. Only two commonly eaten foods constitute complete proteins: eggs and quinoa. Complete protein intake can come from eating a combination of beans, grains, nuts and seeds or tahini as well as supplements such as Bragg’s Amino Acids. As a rule of thumb, one should aim to consume at least 0.35 g of protein per pound of body weight per day.

Clinical relevance: Amino acids are crucial building blocks for key neurotransmitters that affect mood, memory, energy and sleep as well as the production of all proteins utilized in the body. Low levels of amino acids from an insufficient diet and/or hypochlorhydria are associated with a range of common conditions related to impaired production of neurotransmitters including mood disorders, hypoglycemia and insomnia.

Q: What is your preferred source of vitamin B12?

A: Vitamin B12 is produced by bacteria, not plants or animals. There are no natural sources of B12 found in a completely plant-based diet. This means that occult B12 deficiency is far more common in people with vegetarian or near vegetarian diets. Vitamin B12 can be obtained by consuming fortified nutritional yeast and fortified cereals. Supplements also may be required.

Clinical relevance: Vitamin B12 is crucial for nerve and brain cell function and is involved in DNA synthesis and regulation, fatty acid synthesis and energy production. Low levels of B12 are associated with fatigue, depression, cognitive dysfunction, peripheral neuropathy and anemia. Concomitant use of many common medications including antacids, anticonvulsants, antibiotics and metformin may increase the risk of B12 deficiency.

■ Q: What is your preferred source of iron?
A: Iron (for menstruating women or anyone with low iron levels) can be obtained by eating blackstrap molasses, cooked soybeans, lentils, lima beans, quinoa, spinach, Swiss chard, tempeh, tofu and fortified cereals. Iron from these sources, however, is less bioavailable than iron from meat sources. For that reason, vegans and vegetarians require higher iron intake than meat eaters. Clinical relevance: Iron is crucial for blood production and oxygen transportation as well as for numerous enzymatic reactions including the production of dopamine. Low iron is a common cause of fatigue, dizziness, hair loss, irritability, restless legs syndrome, weakness, pica, and brittle or grooved nails. Antacids are one type of medication associated with low iron absorption.

■ Q: What is your preferred source of the long-chain omega-3 fatty acids EPA (eicosapentaenoic acid) and DHA (docosahexaenoic acid)?

A: EPA and DHA are both found in cold water fish such as salmon and sardines. Getting enough of these essential fatty acids can be a challenge for vegetarians. EPA is the long-chain omega-3 fatty acid from which the noninflammatory prostaglandins leukotrienes and thromboxanes come. There is no direct vegetarian source for this 20-carbon chain. Under some circumstances, such as during pregnancy or if consuming a very low-fat diet, the body can make EPA from the shorter-chain (18 carbons long) omega-3 (alpha-linolenic acid) found in walnuts and flax seed.

The 22-carbon DHA is the longest and most polyunsaturated fatty acid in the body. It is critical for proper membrane fluidity (for receptor binding) as well as to the functioning of all cells especially those in the nerves and brain. A vegetarian/vegan form of DHA from algae is commercially available. Patients with significant inflammation may need to supplement with EPA from fish oil or krill oil.

Clinical relevance: Low EPA levels are associated with inflammatory conditions including autoimmune disease, ulcerative colitis, Crohn’s disease and atherosclerosis. Low levels are also associated with increased smooth muscle contraction, asthma, dysmenorrhea, hypertension and irritable bowel syndrome. Low levels are also strongly linked to depression. They also are linked to attention deficit hyperactivity disorder.

Low DHA is associated with cognitive dysfunction (“brain fog”) as well as an increased risk for violence, depression and suicide. DHA is crucial for pregnant and breastfeeding women, as women with lower DHA levels have a much higher incidence of gestational diabetes, hypertension and pre-eclampsia during pregnancy. They also have a much higher incidence of post-partum depression and post-partum obsessive-compulsive disorder.

■ Q: What are your sources of the amino acids tryptophan, methionine and lysine?

A: This is an important question because vegetarian diets are often rich in soybeans and legumes, which are low in tryptophan and methionine. Likewise, diets rich in grains, nuts and seeds will be low in lysine. But eggs, grains and seeds contain tryptophan and methionine. And lysine is found in legumes (beans, peas and peanuts). For these reasons, a combination of foods is needed and supplementation is often required.

Clinical relevance: Tryptophan is the foundation of both serotonin and melatonin. Low serotonin production is associated with antidepressant failure and a number of symptoms including insomnia. Methionine is a crucial sulfur donor for the metabolism of carbohydrates, lipids and amino acids as well as for detoxification and the production of multiple neurotransmitters, insulin, coenzyme A and glutathione. Lysine is crucial for production of proteins and enzymes including pyridoxal phosphate (activated vitamin B6). Lysine is an important adjunct for production of serotonin from 5-hydroxytryptophan (5-HTP). Low lysine is associated with weight loss, anorexia, muscle weakness, poor muscle tone, growth failure in children and anemia.

A: Question for Persons on a Dairy-Free Diet
Many patients report dairy intolerance (as in lactose intolerance or constipation). Others may avoid dairy for different reasons. For example, vegans go beyond a traditional vegetarian diet and do not eat any animal products including eggs and dairy. If a patient says he or she is a vegan, ask all of the questions you would ask a vegetarian plus one more.

■ Q: What are your preferred sources of calcium?
A: Nondairy sources of calcium include almonds, beans, blackstrap molasses, broccoli, dark leafy greens (bok choy, collard greens, kale, mustard greens, turnip greens), dried figs, okra, tahini and tempeh. Note that foods rich in oxalic acid such as chard, collard greens, rhubarb and spinach can bind calcium and reduce its bioavailability. Phytic acid, which is found in many grains, nuts, seeds and vegetables, also can bind calcium. Phytase found in probiotics can block this process. In addition, sprouting grains and seeds as well as cooking foods can increase the bioavailability of calcium in them.

Clinical relevance: Diets low in calcium may result in decreased bone mineral density as calcium must be released from the bones to maintain a normal serum level. Calcium is also crucial in neurotransmitter release and muscle contraction, including cardiac myocyte contraction. Of note, vegetarian and vegan diets are believed to be more alkaline than diets that include meat. This means that, compared with a more acidic animal protein-based diet, a vegan diet may result in less calcium released from the bones to buffer dietary acid loads.

Conclusion
Vegetarian and vegan diets are often manifestations of religious, spiritual and ethical beliefs. Adherence to such diets can be associated with greater longevity and reduced health risks. However, clinicians must be aware of the potential nutritional risks in persons who have not learned, or have not fully applied, the discipline required for healthy menu planning. The questions highlighted in this article enable physicians to better assess how a patient’s vegetarian or vegan diet may be contributing to their health concerns. Their answers can guide further decision-making about both laboratory testing and referrals to a nutritionist or dietitian. MM

Gregory Plotnikoff is an internist at the Penny George Institute for Health and Healing in Minneapolis. He is co-author of the soon-to-be-released book Trust Your Gut (Red Wheel/Conari, 2013).

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