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Vegetarian and Vegan Eating, Honestly: The Ups, the Downs and What to Watch For

By Weight Wire Editorial Team October 4, 2026 Updated November 6, 2026 4 min read
A plate of quinoa, avocado, hummus, tomatoes and cucumber surrounded by fresh peppers, carrots and green beans

Vegetarian and vegan eating is one of the most researched ways of eating, and one of the most misunderstood. This is the second article in our series on popular ways of eating, after the keto diet. Let’s look at the ups, the downs and what to keep in mind if you are curious about eating more plants.

What these diets are

A vegetarian diet leaves out meat, poultry and fish. Many vegetarians still eat eggs and dairy. A vegan diet leaves out all animal products, including eggs, dairy and honey. Both can be built around very different foods, from lentils, vegetables and whole grains to chips, soda and meat substitutes, and that range matters a lot for health.

The ups and the downs

What the evidence reports as upsides What to keep in mind
A major dietetics position paper says well-planned vegetarian and vegan diets are healthful and nutritionally adequate, and are linked with lower risk of heart disease, type 2 diabetes, high blood pressure and obesity. “Well planned” is doing a lot of work. The same paper says vegans need a reliable source of vitamin B12, from fortified foods or supplements.
In a meta-analysis of 12 trials (1,151 people, median 18 weeks), people assigned to vegetarian diets lost about 2 kg more than those on non-vegetarian diets. That is a modest, short-term difference, and the result for lacto-ovo vegetarian diets was not statistically clear on its own.
The vegan-only trials in that review showed the largest difference, about 2.5 kg more weight loss. Trials last months, not years, so we know less about the long run.
Diets rich in vegetables, fruit, whole grains, beans, nuts and seeds tend to be higher in fiber and lower in saturated fat. A vegan or vegetarian diet can still be heavy in refined carbohydrates, sweets and ultra-processed foods.

Weight loss on plant-based diets

In the meta-analysis by Huang and colleagues, published in 2016, vegetarian diets led to an average of about 2 kg (roughly 4.5 pounds) more weight loss than non-vegetarian diets, with vegan diets at about 2.5 kg. These were trials in which people were assigned to a diet, which is stronger evidence than comparing people who happen to eat differently. The trials were fairly short and the diets and comparison groups varied, so the safest conclusion is that a plant-based eating pattern can support weight loss, though it does not guarantee it.

Things to watch for

  • Vitamin B12. Harvard’s Nutrition Source notes that people who avoid meat, fish, poultry and dairy are at risk of deficiency, because B12 is found naturally only in animal foods. Fortified foods, such as fortified nutritional yeast, some breakfast cereals and enriched soy or rice milks, or a supplement are the usual answer.
  • Protein. It is easy to get enough from beans, lentils, tofu, tempeh and dairy or eggs, but it takes a little planning. Our guide to how much protein you need gives the current range.
  • Other nutrients. Dietitians commonly check iron, calcium, zinc, iodine and omega-3 fats on plant-based plans. A blood test and a conversation with a registered dietitian can show whether you need more of any of these.
  • Convenience foods. Plant-based does not automatically mean minimally processed. Our look at ultra-processed foods and weight explains why that matters.

Who should talk to a professional first

Please speak to a doctor or registered dietitian before changing how you eat if you are pregnant or breastfeeding, planning a pregnancy, have a chronic condition such as diabetes or kidney disease, take medications that affect nutrient absorption, are feeding a child, or have any history of disordered eating. The position paper says well-planned vegetarian and vegan diets can suit all stages of life, but “well-planned” is the key phrase, especially for children and during pregnancy.

A simple way to try it

  1. Pick one or two plant-based dinners a week and build them around beans, lentils, tofu or tempeh.
  2. Add vegetables to every meal, and choose whole grains over refined ones where you can.
  3. If you go fully vegan, set up a B12 source from the start.
  4. Check in with a dietitian after a couple of months.

The big picture

Vegetarian and vegan diets have a strong record: they are well-studied, can be nutritionally complete, and are linked with modest weight loss and several health benefits. Their weak spots are nutrients such as B12, and the fact that “plant-based” can still mean a lot of processed food. Done thoughtfully, they are one of several well-researched ways to eat, and a few more plants on your plate is a lovely place to begin. Next in the series: the carnivore diet.

Sources

  1. Craig WJ, Melina V, Levin S. Position of the Academy of Nutrition and Dietetics: vegetarian diets. Journal of the Academy of Nutrition and Dietetics, 2016;116(12):1970-1980. Abstract
  2. Huang RY, Huang CC, Hu FB, Chavarro JE. Vegetarian diets and weight reduction: a meta-analysis of randomized controlled trials. Journal of General Internal Medicine, 2016. Summary record
  3. Harvard T.H. Chan School of Public Health, The Nutrition Source. Vitamin B12. Harvard Nutrition Source
Not medical advice. This article is for education only. Review any weight loss, health, diet, fitness or medication decision with your doctor or primary care physician first. Medical disclaimer.

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Weight Wire Editorial Team

Writer at Weight Wire.

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