What happens to your body when you first become vegetarian?

October 21, 2025 •

6 min read

Research has found that a significant shift in gut bacteria can occur just days after adopting a plant-based diet. This is just one of many ways your body responds to the change, offering a direct answer to the question: What happens to your body when you first become vegetarian? Understanding these early adjustments can help you navigate the transition smoothly.

Quick Summary

As your diet transitions to vegetarian, your body's initial response involves notable digestive and energy shifts. While fiber and nutrient intake increases, you may experience temporary bloating or fatigue as your gut adjusts. Long-term health markers like cholesterol and blood pressure can improve, though careful nutritional planning is key to sustaining benefits and preventing deficiencies.

Key Points

Initial Digestive Adjustment: An increase in dietary fiber can cause temporary gas and bloating, but it helps foster a healthier gut microbiome in the long run.
Energy Fluctuations: You may experience an initial boost of energy or temporary fatigue; ensure adequate calorie intake from nuts, seeds, and legumes to avoid feeling sluggish.
Nutrient Monitoring: Pay close attention to nutrients primarily found in animal products, such as Vitamin B12, iron, and Omega-3 fatty acids, and plan to include fortified foods or supplements.
Psychological Cravings: Cravings for old foods are normal, but exploring new recipes and focusing on the positive aspects can help manage them effectively.
Holistic Benefits: Over time, a balanced vegetarian diet can lead to lower cholesterol, blood pressure, and better overall cardiovascular health, along with improved skin and mental well-being.
Strategic Transition: Gradually incorporating vegetarian meals and focusing on whole foods rather than processed junk can ease the transition and prevent common pitfalls.

The Initial Shift: Your Body's First Response

When you first become a vegetarian, your body begins a process of adaptation. The most immediate changes often occur in your digestive system and energy levels as your intake of dietary fiber increases and meat protein is eliminated. For some, this period is marked by a noticeable feeling of lightness and increased energy, while others may experience temporary discomfort. The key to navigating this phase is understanding what to expect and ensuring your new diet is well-balanced to support your body's changing needs.

Digestive Changes and Gut Health

One of the most profound and rapid changes when transitioning to a vegetarian diet is the effect on your gut microbiome. A plant-heavy diet is rich in fiber, which feeds beneficial gut bacteria that specialize in breaking down plant matter.

Increased Fiber Intake: A vegetarian diet typically contains significantly more fiber than a meat-based diet. While this is great for promoting regular bowel movements and improving digestion over time, the sudden influx can lead to temporary side effects like gas and bloating.
Gut Microbiome Shift: As your gut bacteria adapt to the new diet, the balance of microbes shifts. Studies have shown a reduction in inflammatory bacteria and an increase in beneficial bacteria that ferment fiber into short-chain fatty acids (SCFAs), which support gut and overall health.

Energy Levels and Potential Fatigue

For many, the first few weeks can involve fluctuations in energy levels. Some people report feeling more energized, potentially because plant-based foods are often lighter and require less energy to digest than meat. However, it is also common to experience temporary fatigue, especially during a sudden switch.

Several factors can contribute to initial fatigue:

Caloric Density: Plant-based foods are often less calorically dense than meat, so you may be unintentionally eating fewer calories than your body needs. It is important to ensure you are eating enough food and incorporating calorie-dense plant-based sources like nuts, seeds, and avocados.
Nutrient Gaps: The transition can sometimes lead to lower-than-usual levels of iron and vitamin B12, both critical for energy production. This can be easily remedied by focusing on iron-rich plant foods and considering B12 supplementation.

Cravings and Mental Adjustment

Switching dietary habits can be a psychological as well as a physiological challenge. Cravings for meat or familiar processed foods are not uncommon. A poorly managed vegetarian diet, rich in processed vegan junk food, can be just as unhealthy as a poor omnivorous diet. A thoughtful approach, with a focus on trying new flavors and recipes, can make the transition a more positive experience. Additionally, some studies have explored the link between diet and mood, noting that a nutrient-rich plant-based diet can support mental well-being, while deficiencies can have the opposite effect.

Long-Term Benefits and Sustaining Health

Beyond the initial adjustment phase, a well-planned vegetarian diet can lead to a host of significant health improvements that support long-term well-being.

Improved Cardiovascular Health and Weight Management

Vegetarians often consume less saturated fat and cholesterol than omnivores, which can have a protective effect on heart health. Research consistently links vegetarian diets with lower LDL (bad) cholesterol, lower blood pressure, and a reduced risk of cardiovascular disease. In addition, the increased fiber intake and lower overall calorie density of many plant-based foods can support weight loss and help maintain a healthy body weight.

Skin and Overall Well-being

The increased consumption of fruits and vegetables means higher antioxidant and vitamin intake, which can lead to clearer, healthier skin. The reduction in processed foods and saturated fats also reduces systemic inflammation, which benefits the immune system and overall vitality. Many long-term vegetarians report feeling more energetic and having better overall health than they did on a meat-based diet.

Navigating Potential Nutrient Deficiencies

To maximize the benefits of a vegetarian diet, it is crucial to pay attention to nutrients that are less abundant in plant-based foods.

Vitamin B12: Found almost exclusively in animal products, B12 is essential for nerve function and energy. Supplementation or consuming fortified foods is highly recommended for all vegetarians, especially vegans.
Iron: Plant-based (non-heme) iron is not absorbed as efficiently as heme iron from meat. However, eating iron-rich plant foods like lentils, beans, and leafy greens with a source of vitamin C can significantly enhance absorption.
Zinc: Phytates in whole grains and legumes can inhibit zinc absorption. Soaking and sprouting legumes can help, and good sources include nuts, seeds, and fortified cereals.
Omega-3 Fatty Acids: DHA and EPA are mainly found in fish. While the body can convert ALA (from flaxseed, walnuts, and canola oil) to DHA and EPA, this is not very efficient. Algae-based supplements are an option to ensure adequate intake.
Calcium and Vitamin D: Vegans may have lower calcium intake, while vitamin D levels can drop in those limiting dairy. Fortified plant milks, leafy greens, and supplements can help maintain adequate levels.

Poorly Planned vs. Well-Planned Vegetarian Diets

Not all vegetarian diets are created equal. The health outcomes depend heavily on the quality of food choices.


Feature	Poorly Planned Vegetarian Diet	Well-Planned Vegetarian Diet
Food Choices	Relies on processed snacks, sugary treats, and refined carbs like white pasta and bread.	Focuses on whole grains, legumes, vegetables, fruits, nuts, and seeds.
Nutrient Intake	High risk of deficiencies in B12, iron, zinc, and omega-3s. Low in essential vitamins and minerals.	Balanced and nutrient-dense, with a focus on sourcing and supplementing key nutrients.
Health Outcomes	Can still lead to weight gain, inflammation, and potential cardiovascular risk due to unhealthy fats and sugar.	Associated with lower body mass index, reduced risk of heart disease, and improved health markers.
Satiety	Can leave you feeling hungry or unsatisfied due to low fiber and high sugar content.	High fiber and protein from whole foods promote fullness and prevent overeating.
Digestion	Can cause bloating and digestive issues if fiber is added improperly or if relying on processed foods.	Supports a healthy and diverse gut microbiome, leading to regular and healthier bowel function.

Tips for a Smooth Transition

To ensure a positive experience and reap the benefits of your new diet, consider these strategies:

Transition Gradually: Instead of going 'cold turkey', try a gradual approach. Start by incorporating one vegetarian meal per week and slowly increase the frequency.
Plan Your Meals: Research and plan your meals to ensure they are varied and include all essential nutrients. Using a cookbook or meal planning app can be helpful.
Incorporate New Foods: Explore new protein sources like lentils, chickpeas, and tofu. Focus on consuming a wide variety of colorful fruits and vegetables.
Hydrate and Listen to Your Body: Drink plenty of water, especially as your fiber intake increases. Pay attention to how your body feels and adjust your meals accordingly.
Consider Supplements: Discuss potential nutrient gaps with a healthcare professional and consider taking a B12 supplement as a safety measure.
Get Support: Connect with a community of other vegetarians online or locally for tips, recipes, and encouragement. For further nutritional guidance, resources like the Academy of Nutrition and Dietetics provide trusted information.

Conclusion

When you first become vegetarian, your body embarks on a period of adjustment marked by changes in digestion, energy, and mental state. While some initial discomfort is possible due to shifts in gut flora and nutrient intake, these are typically temporary. A well-planned and balanced approach to vegetarianism, focusing on whole, nutrient-dense foods, can lead to significant long-term health benefits, including improved cardiovascular health, better weight management, and enhanced overall vitality. Understanding and proactively managing the initial phase is the best way to ensure a successful and rewarding transition to your new diet.

Visit the Academy of Nutrition and Dietetics for more information on vegetarian diets.

Frequently Asked Questions

Yes, it is very common to experience more gas and bloating when you first become vegetarian. Your body, and especially your gut bacteria, need time to adjust to the significant increase in dietary fiber from fruits, vegetables, and legumes.

You may feel tired initially for a few reasons. A sudden change in diet can alter your caloric intake, and you may not be eating enough. Additionally, meat is a primary source of heme iron and Vitamin B12, so a deficiency in these nutrients can cause fatigue if not managed correctly.

There are plenty of vegetarian protein sources. Include a variety of legumes (beans, lentils), soy products (tofu, tempeh), nuts, seeds, and whole grains in your meals. Many vegetarians also consume eggs and dairy for additional protein.

Yes, it is highly recommended to take a Vitamin B12 supplement or consume foods fortified with B12, such as some soy milks and breakfast cereals. This vitamin is naturally found almost exclusively in animal products, and long-term deficiency can lead to serious health issues.

A well-planned vegetarian diet, rich in fiber and whole plant foods, has been shown to improve gut health and diversify the gut microbiome over time. This leads to beneficial outcomes like reduced inflammation and better digestive function.

Many people find that they lose weight on a vegetarian diet, primarily because plant-based foods tend to be lower in calories and higher in fiber, which promotes satiety. However, weight loss depends on eating a healthy, balanced diet and not replacing meat with processed junk food.

Studies have shown that vegetarians generally have lower total and LDL ('bad') cholesterol, as well as lower blood pressure than non-vegetarians. This is linked to lower intake of saturated fat and cholesterol, along with higher intake of fiber and plant nutrients.