This guide explains how to combine intermittent fasting with a vegan or plant-based diet: how much protein to aim for, the most protein-dense plant foods, a sample day of eating, the nutrients that need extra attention, supplements worth considering, and which fasting schedules fit best.
Intermittent fasting can work on a plant-based diet, but it takes more planning. Many plant proteins are less concentrated than animal proteins, so you need more food volume to get the same amount, and a shorter eating window leaves less time to eat it. Without a plan, it is easy to fall short on protein and calories.
Table of Contents
Why Vegan Fasting Is Harder
The challenge has two parts: protein density and amino acid completeness.
Density
As a rough comparison, 150 g of cooked chicken breast provides about 45 g of protein in about 250 calories. Getting the same 45 g from cooked lentils takes about 500 g of lentils and roughly 550-600 calories. Getting 100 g of protein a day from lentils alone would mean more than 1 kg of cooked lentils — a lot of food for one or two meals.
Tofu, tempeh, seitan, and textured vegetable protein (TVP) are more concentrated than beans and lentils. Mixing sources (legumes, soy foods, grains, seeds, and possibly a protein powder) makes the numbers work much more easily than relying on one food.
Completeness
Animal proteins contain all nine essential amino acids in proportions close to human needs. Many individual plant proteins are relatively low in one or two (legumes tend to be lower in methionine, grains in lysine), while soy is closer to animal proteins. This isn’t a problem if you eat a variety of plant proteins across the day.
Note: the old idea that you must combine proteins within a single meal is outdated. Combining across the day is sufficient.
Protein Targets and Plant Adjustments
Protein needs are the same whether or not you fast; the challenge is fitting them into a shorter window. Common reference points:
- General adult reference intake: about 0.8 g protein per kg of body weight per day
- Older adults, or during weight loss: many experts suggest aiming somewhat higher
- Regular resistance training or intense exercise: sports nutrition guidance commonly suggests roughly 1.2-2.0 g per kg per day
If you have kidney disease, ask your doctor what protein intake is right for you.
Plant-protein adjustment
Plant proteins are, on average, slightly less digestible than animal proteins, and their amino acid profiles differ. For that reason, some people on fully plant-based diets aim a little higher within these ranges, especially if they are trying to build or keep muscle.
Per-meal target
With only two or three meals, it helps to include a substantial protein source in each, often in the range of 20-40 g depending on your size and total needs. Leucine is an amino acid closely linked to muscle building; soy foods, seitan, lentils, and plant protein powders are useful sources.
The Densest Plant Protein Sources
Soy products (highest density, complete protein)
- Firm tofu: ~12–17 g protein per 100 g (varies by brand and firmness)
- Tempeh: ~19-20 g protein per 100 g
- Edamame: ~11 g protein per 100 g (cooked)
- Soy milk: ~3.5 g protein per 100 ml
- TVP (textured vegetable protein): ~50 g protein per 100 g dry
Seitan (very high density, but incomplete)
- Seitan: often around 25 g protein per 100 g, depending on the recipe. Made from wheat gluten, so it is not suitable for people with coeliac disease. Low in lysine, so combine with legumes across the day.
Legumes
- Lentils: 9 g protein per 100 g cooked
- Chickpeas: 8 g protein per 100 g cooked
- Black beans: 9 g protein per 100 g cooked
- Kidney beans: 9 g protein per 100 g cooked
- Split peas: 8 g protein per 100 g cooked
Nuts and seeds
- Hemp seeds (shelled): ~30 g per 100 g, also a source of plant omega-3 (ALA)
- Pumpkin seeds (shelled): ~30 g per 100 g
- Almonds: 21 g per 100 g
- Peanuts and peanut butter: 25 g per 100 g
- Chia seeds: 17 g per 100 g
Grains (modest, but contribute when combined)
- Quinoa: 4 g per 100 g cooked — complete protein
- Oats: 12 g per 100 g dry
- Wholewheat pasta: 5 g per 100 g cooked
Plant protein powders
- Pea protein: typically around 20-25 g per scoop (check the label); relatively low in methionine
- Soy protein: typically around 20-25 g per scoop
- Pea and rice blends: combine to give a more balanced amino acid profile
- Hemp protein: lower in protein per scoop but contains fibre
Sample Vegan 16:8 Day (Around 100 g Protein)
Protein figures below are approximate and depend on brands and portion sizes.
First meal — 12:00 PM (~45 g protein)
- Tofu scramble: 200 g firm tofu (~30 g protein) with onions, peppers, spinach, and turmeric
- 2 slices wholegrain toast (~8 g)
- 1 tablespoon hemp seeds (~3 g)
- Tahini drizzle (~2-3 g)
- Fruit on the side
Snack — 3:30 PM (~20-25 g protein)
- Soy or pea protein shake made with soy milk, or soy yogurt topped with hemp seeds
Second meal — 7:30 PM (~35-40 g protein)
- Lentil and chickpea curry: 150 g cooked lentils + 100 g cooked chickpeas (~13 + 8 g)
- A portion of brown rice (~4 g)
- Steamed broccoli
- 50 g tempeh strips on the side (~10 g)
- A sprinkle of cashews (~2-4 g)
Total: roughly 100-110 g of protein, with a good mix of amino acids across the day. Reaching this level takes planning; without the soy foods and the shake, the total would be considerably lower. Adjust portions to your own protein and energy needs.
Micronutrients to Watch
These nutrients need deliberate attention on any vegan diet. With fewer meals in a shorter window, it is even more important to plan for them. If you’re unsure, a registered dietitian or your doctor can advise on blood tests and supplements.
Vitamin B12
Plant foods don’t provide reliable amounts of B12, so vegans need fortified foods or a supplement. Follow the dosing on a reputable product or the advice of your healthcare provider. Long-term B12 deficiency can cause anaemia and nerve damage that may be permanent, so this is essential, not optional.
Iron
Plant iron (non-haem) is less bioavailable than animal iron. Pair iron-rich foods (lentils, tofu, dark leafy greens) with vitamin C (peppers, citrus, tomatoes) at the same meal to improve absorption. Avoid coffee and tea within 1–2 hours of iron-containing meals.
Zinc
Lower bioavailability from plant sources. Pumpkin seeds, lentils, chickpeas, cashews, and oats are reasonable sources. Soaking and sprouting legumes improves zinc absorption.
Calcium
Good sources include calcium-set tofu, fortified plant milks and yogurts, tahini, kale, and broccoli. Adult recommendations are commonly around 700-1,000 mg per day, depending on country, age, and sex.
Iodine
Plant diets can be low in iodine. Options include iodised salt, fortified plant milks, or a supplement. Seaweed varies enormously in iodine content, and some types (especially kelp) can provide too much.
Omega-3 (DHA and EPA)
Plant omega-3 (ALA from flax, chia, walnuts, and hemp) is converted only in small amounts to the longer-chain forms DHA and EPA. Algal oil supplements provide DHA and EPA without animal sources, and some vegans choose to take one.
Vitamin D
Many people, vegan or not, need a vitamin D supplement at least during months with little sunlight, depending on where they live. Follow your local health guidance. Vegan vitamin D3 (from lichen) and D2 are available.
Choline
Choline intake can be low on vegan diets. Soy foods, beans, broccoli, and quinoa contribute. Discuss a supplement with a dietitian if your diet is limited.
Supplements to Consider
Check with your doctor or pharmacist before starting supplements, especially if you take medication or are pregnant.
Generally recommended for vegans
- Vitamin B12 (essential)
- Vitamin D, depending on sunlight exposure and local guidance
- Iodine, if you don’t use iodised salt or fortified foods
Worth considering
- Algal DHA/EPA
- Pea or soy protein powder, if you struggle to meet protein needs from food
- Iron or zinc, only if blood tests show you need them (too much iron can be harmful)
- Choline, if your diet is limited
- Creatine, which some vegans who train use because diets without meat and fish contain almost none
Usually unnecessary
- Greens powders
- “Superfood” blends
- BCAA products, if you’re already eating enough protein
Which Protocols Suit Vegan Eating
Common Mistakes
Estimating protein by feel rather than tracking
Plant-based meals can look filling and protein-rich but contain less protein than expected. Tracking your intake for a week or two is a simple way to check whether you are meeting your needs.
Relying on nuts as a protein source
Nuts are mostly fat. A handful of almonds is ~6 g protein and ~170 calories. Useful as a fat source; insufficient as a primary protein.
Skipping fortified foods
Fortified plant milks, fortified breakfast cereals, and fortified nutritional yeast can help with B12, calcium, and other vitamins. Avoiding all fortified products makes you more reliant on supplements.
Treating protein powder as cheating
Pea, soy, or blended plant protein powders are concentrated plant protein. They are not required, but they can make meeting protein needs in a short eating window much easier. Choose products that are third-party tested where possible.
Eating very low-fat
Some vegan styles emphasise very low fat (e.g., whole-food plant-based with no oil). In a compressed eating window, this often means inadequate calories. Olive oil, nuts, seeds, tahini, and avocados deliver calories that grains and vegetables alone often can’t provide in the time available.
Soy avoidance based on outdated concerns
Soy is one of the most useful protein sources for vegans. Current evidence generally does not support concerns that normal dietary amounts of soy foods harm hormone health in healthy adults. Tofu, tempeh, edamame, and soy milk are reasonable staples. If you have a thyroid condition, take thyroid medication at the time your doctor advises, as soy can affect its absorption.
Frequently Asked Questions
Will I lose muscle on vegan IF?
Eating enough protein and overall calories, and doing regular resistance training, are the best ways to limit muscle loss on any diet. This takes more planning on a vegan diet, but some studies suggest that when protein intake is adequate, muscle and strength gains from training can be similar to those on omnivorous diets.
Is “eating one big meal of plants” (vegan OMAD) viable?
It is difficult. You would need to rely heavily on tofu, tempeh, seitan, lentils, and protein powder to get enough protein in one meal. For most people, vegan OMAD is more realistic as an occasional practice than a daily one. See our OMAD guide.
Should I take BCAAs?
If you’re eating enough protein, BCAA supplements are unlikely to add much. If you’re struggling to get enough protein, a complete protein powder is usually more useful.
What about pea protein vs whey for ex-omnivores?
Whey contains somewhat more leucine per gram and is digested quickly. Plant protein blends can come reasonably close, particularly in slightly larger servings. For people eating enough protein overall, the practical difference is likely to be small.
Are plant-based meat alternatives useful?
They can be convenient, and many provide a useful amount of protein. They are often highly processed and can be high in salt, so check labels and treat them as one option among many rather than a daily staple.
I’m vegan and feel terrible on 16:8. What might be wrong?
Common causes include not eating enough protein or calories, not getting enough salt and fluids, and deficiencies such as B12 or iron. Track your intake for a week or two, talk to your doctor about blood tests, and consider a gentler schedule such as 12:12 or 14:10. If you still feel unwell, fasting may simply not suit you, and that’s fine.
The Bottom Line
Intermittent fasting can fit a vegan diet, but it needs more planning than on an omnivorous diet. Protein is usually the main challenge, so build meals around soy foods and legumes, consider a protein powder if needed, and track your intake for the first few weeks. Make sure you have reliable sources of B12, and consider vitamin D, iodine, and algal omega-3. Choose an eating window long enough to eat everything you need; for most people, 14:10 or 16:8 works better than shorter windows. If you have health conditions or take medication, talk to your healthcare provider first.