Thinking of Quitting Your Vegan Diet? Doctors Address 5 Common Health Questions


12 Minutes Read

Mauricio Gonzalez MD, Michelle McMacken MD, Danielle Belardo MD, and Robert Ostfeld, MD, MSc - Media Credit:

In recent months the plant-based community has been rocked by a number of ‘influencers’ revealing that they have gone back to eating meat, dairy, and eggs, blaming the negative health impact of their diets.

But according to a group of the world’s leading plant-based doctors, a diet free from all animal products can be one of healthiest around. These doctors tackle some of the most common questions around vegan diets – and give their expert advice on health. 

How can I prevent B12 deficiency?

By Mauricio Gonzalez, MD

Did you hear your friend complaining about the lack of vitamin B-12 on a plant-based diet? Here are some facts that can help to guide you (and your friend) to robust health following plant-based nutrition. Vitamin B12 is present in some foods like meat, eggs, and dairy, added to others, and accessible as a supplement as well.

It is a responsibility for all of us who are following a healthy vegan diet, to add this nutrient in the form of a supplement. Why? B-12 is required for proper red blood cell formation, neurological function, and DNA synthesis.

First of all, you should consult a medical professional if you are worried that you might have a B-12 deficiency. Why? There are many reasons why someone might be lacking this important nutrient such as autoimmune diseases or concomitant use of necessary medications. Also, your doctor can help you decide the right dose of B12 if you are deficient.

Now, back to the matter at hand. Let us say today is your first day on a plant-based diet (if that is the case, congratulations!). Now, what is recommended daily intake of B12?

B12 dose

As you can see it is a pretty small dose, but truly important! there are many different types of vitamin b12 in the market. But, you need not worry as there is no superior form. Although it is fair to say that most studies analyzed cyanocobalamin, which is cheap and worldwide available.

Now, most of the supplements have large doses such as 500 or sometimes 1,000mcg. Why? Well, this vitamin has a highly complex absorption mechanism. If a healthy person takes 500mcg, only 10mcg will be absorbed. Therefore, not everything you take will be absorbed. But do not worry, I will give you specific recommendations about doses at the end of this article.

Now, you are going to hear that ONLY VEGANS suffer from this deficiency. But reputable studies have shown that its prevalence is significant in young adults in the general population.In other words, everybody should be worried about this.

How do you know if you are deficient? As I pointed out earlier, seek medical advice. Your doctor might choose to check b12 blood, homocysteine or methylmalonic acid levels. If you add a b12 supplement to your already healthy plant-based diet, you are potentiating its benefits. Is this not amazing and reassuring? Now, let me be more practical about how much to take.

?Recommended doses for maintaining healthy B12 levels: Daily or Weekly Options

Just bear in mind that these recommendations are for people who have normal B12 values. If you are deficient, you will need higher doses. Hope this information helps you thrive in your plant-based journey! ?

Why am I having gas and bloating?

By Michelle McMacken, MD?

Gastrointestinal symptoms such as bloating, gas, and abdominal pain are common, accounting for an estimated 16 million visits to primary care practitioners in the United States alone. The vast majority of those affected eat an omnivorous diet. But it is true that a plant-based diet can sometimes cause gas, bloating, and gastrointestinal discomfort. Why does this happen? And is going back to animal products the answer?

Of course, you should always consult a qualified physician or other health professional for a medical evaluation if you’re not feeling well. Ideally, you would see someone knowledgeable in plant-based nutrition; lists of plant-based health professionals are available at

But let’s get back to our questions. Why might a plant-based diet cause gastrointestinal symptoms? A healthful plant-based diet is high in fiber, typically more than 35 grams per day, compared with the average 15 grams per day on a standard American diet. Fiber is one of the most beneficial nutrients we can consume – it promotes favorable shifts in our gut bacterial patterns, allows gut bacteria to make short-chain fatty acids and other protective nutrients, and of course helps prevent constipation. It’s also been linked to dramatic decreases in the risk of type 2 diabetes, heart disease, high blood pressure, high cholesterol, obesity, and certain cancers.

Fiber and bloating

However, fiber can cause bloating and discomfort when it gets fermented by bacteria in the large intestine, releasing gas. This is a normal and healthy process, but it can be uncomfortable, especially if fiber is increased too quickly in the diet. If you are transitioning to a plant-based diet, it’s a good idea to ramp up dietary fiber slowly, over a few weeks to months. If you are already plant-based, try these tips: switch from larger beans to split peas, lentils, tofu, chickpeas, or tempeh, then slowly reintroduce larger beans; reduce your portions of beans to 1/4 cup a day, and gradually work your way back up to larger portions; double soak dry beans and make sure to rinse canned beans.

Sometimes a low-FODMAP diet is advised to reduce gas and discomfort, especially for people with irritable bowel syndrome. FODMAPs (fermentable oligo-, di-, mono-saccharides & polyols) are small carbohydrates that are fermented in the gut and can cause bloating. Examples of high-FODMAP foods include dairy products, apples, onions, garlic, artichokes, wheat, and most beans. The goal of the low-FODMAP approach is to temporarily avoid high-FODMAP foods and then gradually reintroduce them.

Low FODMAP is not along-term, or even medium-term, diet. High-FODMAP plant foods should not be avoided for long periods of time. They are actually some of the healthiest foods around, since they help our gut bacteria make short-chain fatty acids, which reduce inflammation, protect the intestinal lining, and increase insulin sensitivity. Trying low-FODMAP does not mean you have to give up a plant-based diet, but it is critical that anyone trying a low-FODMAP diet do so under the guidance of an experienced dietitian and/or other knowledgeable health care professional.

Another condition that can cause bloating and abdominal discomfort is SIBO (small intestinal bacterial overgrowth), in which there are excessive numbers of bacteria in the small intestine. There are several key risk factors for SIBO (including anatomic issues, the use of certain medications, and the presence of underlying conditions that affect movement of food through the intestine), but a plant-based diet isn’t one of them. Tests are available to evaluate for SIBO.Treatment typically involves using antibiotics to reduce the bacterial overgrowth as well as addressing the underlying cause, if possible. Plant-based diets are NOT a known cause of SIBO, and eating animal products is not an established treatment for this condition. If you are concerned that you might have SIBO, you should see a knowledgeable health professional for proper evaluation and treatment. ?

Fiber can cause bloating (Photo: Adobe. Do not use without permission)

Did my friend lose her period because of her plant-based diet?

By Danielle Belardo, MD

So…you find out that your friend who went vegan lost her period! It must be because of the lack of meat, dairy, eggs, fish, or animal protein, right?

False.There is absolutely nothing specific in animal products that helps promote fertility or regulate menstrual cycles.

First of all, what is amenorrhea? It’s the absence of menses aka your period, and it can be caused by a variety of reasons. It can be a transient, intermittent, or permanent condition, and it can result from dysfunction of the hypothalamus, pituitary, ovaries, uterus, or vagina. So most importantly, every woman with new-onset amenorrhea should be evaluated by a physician, including a thorough history and physical examination, bloodwork, assessment of estrogen status, and, in some cases, imaging.

But let’s say pregnancy and other etiologies of amenorrhea have been ruled out. If a change in diet causes a loss of menses, this is considered ‘functional hypothalamic amenorrhea’, or FHA.


So why did this happen to your friend who went plant-based? Likely because she was not consuming enough calories, or was expending too much energy. This can happen on ANY diet, whether it is an omnivore diet, vegan diet, or keto diet. Low energy availability from decreased caloric intake, excessive working out, or both, as well as stress, are common causes of secondary amenorrhea in women.

Too little calories can lead to a disruption of pulsatile hypothalamic gonadotropin-releasing hormone secretion, which leads to absent mid-cycle surges in luteinizing hormone secretion, absence of normal follicular development, an ovulation, and low serumestradiol concentrations. Once diagnosed with FHA, treatment focuses on consuming enough calories and increasing body weight appropriately.

For the restoration of menses and improvement in bone density, the goal should be to increase caloric intake and work to increase body weight if less than 90 percent of ideal body weight. Some individuals may need to cut back on exercise as well.

So how can you increase your calories on a whole food plant-based diet? For starters, increase your overall portion sizes and intake! Add more snacks throughout the day. Smoothies can be an easy way to add more calories to your diet. If you find you’re getting too full at each meal, focus on incorporating more calorie dense foods into your diet, such as adding nuts and nut butters, seeds, or avocado.

But above all, it is incredibly important to be evaluated by a physician to receive the appropriate evaluation and treatment, as various eating disorders can be a cause of low body weight and functional hypothalamic amenorrhea regardless of dietary preference. Women reversing the state of low body weight from low calorie intake need to be followed closely for three to six months to determine if their menstrual cycle resumes, otherwise, further intervention (either psychological or otherwise) may be required to help aid in recovery.

There is nothing in animal foods that specifically promotes fertility (Photo: Adobe. Do not use without permission)

Don’t I need meat to get iron?

By Michelle McMacken, MD

?The heme form of iron, found in meats, is more readily absorbed – but this isn’t necessarily good. It means we tend to store iron even when our bodies don’t need it. That’s a problem because heme iron is a pro-oxidant molecule that can form carcinogens and cause DNA damage, oxidative stress, and inflammation. Higher iron stores correlate with a higher risk of type 2 diabetes, cancer, heart disease, and premature mortality. In a recent study of >500,000 adults, heme iron was strongly linked to death from nine different causes.

In contrast, when we get iron from plants (non-heme iron), our bodies are better able to regulate absorption – if our iron stores are low, we absorb more, and vice-versa. People eating plant-based diets can adapt over time to absorb more iron. Non-heme iron has not been tied to chronic diseases, and of course, it typically comes with the many beneficial phytonutrients found in plant foods.

Iron is abundant in many plant foods, including lentils, beans (especially soy), spinach, oatmeal, quinoa, and seeds. Phytates in some plant foods can decrease absorption, but this can be overcome by pairing these foods with vitamin C or citrus. Indeed, 50mg of vitamin C (eg, 3/4 cup broccoli, Brussels sprouts, cauliflower, collards, bell peppers, cantaloupe, citrus fruits, papaya, or strawberries) raises iron absorption four-six fold.

To maximize iron absorption, avoid drinking coffee and tea with meals. These beverages inhibit absorption, as do calcium supplements; consume them at least an hour apart from iron sources. Dairy also lowers iron absorption.

Most research shows that vegans and vegetarians are no more likely to have iron-deficiency anemia than omnivores. In fact, vegans consume as much or more iron than omnivores.Moderate to severe iron-deficiency anemia may require treatment with iron supplements, but only with the advice of a health professional. If you have iron-deficiency anemia, it is critical to find out why. The cause is almost never a well-planned plant-based diet; more commonly it’s menstrual blood loss, gastrointestinal bleeding, or other health issues.

I feel fatigued. Is it my diet?

By Robert Ostfeld, MD, MSc?

As plant-based physicians, we have had the opportunity to see hundreds of patients thrive on a plant-based diet. However, one increasingly common concern we have been hearing, is that people may feel fatigued or tired on a plant-based diet.

So, what’s the disconnect?

In our experience, increased fatigue on a plant-based diet happens rarely and is usually related to low caloric intake, which means you are not eating enough. Although a plant-based diet is incredibly nutrient dense, it is not calorically dense, particularly if someone is consuming primarily fruits and vegetables. So it is quite possible that people who have transitioned to a plant-based diet may not be meeting their caloric needs, and hence feel fatigued.

If you experience fatigue while on a plant-based diet, you can eat a higher volume of food and/or more calorically dense foods like nuts, seeds, whole grains, lentils and/or avocados. In my clinical experience, consuming greater quantities of those foods usually does the trick. What a great ‘problem’ to have. (Full disclosure: I routinely have three servings at dinner).

It is also important to get evaluated by your physician for conditions that can cause fatigue that may be unrelated to your diet, such as infections, endocrine disorders, and other issues. It can be tempting to ‘blame’ any number of issues on a plant-based diet and we definitely do not want to miss a non-diet related medical condition. Furthermore, your physician may be able to provide helpful dietary guidance. And, reassuringly, studies have shown that consuming more plant-based foods can actually improve fatigue.

There are diet-related issues to stay vigilant about, as well. For example, anemia can make you feel fatigued. Although iron deficiency anemia is typically no more likely to occur in vegetarians than non-vegetarians, screening for iron levels is important if you feel fatigues. And, screening for vitamin B12 deficiency and routine B12 supplementation is important, too.

The great news is that by eating a plant-based diet you are getting healthier. And, fighting fatigue may be as simple as eating even more amazing plant-based foods.


How can I prevent B12 deficiency?

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