The number of people choosing a vegan diet is growing rapidly. In the UK, the vegan population tripled between 2014 and 2019 (1), and jumped by another 1.1 million between 2023 and 2024 (2).
Health bodies increasingly support this way of eating (3, 4, 5), and for good reason. Diets rich in whole plant foods have been linked with lower risk of cardiovascular disease (6), dementia (7), cancer (8), type 2 diabetes (9), obesity (10), and even depression (11). Plenty of athletes are also attributing improved performance and recovery to going plant-based.
But there’s a common issue I often hear about — feeling tired or low in energy on a vegan diet.
So, what’s behind it?
Just because something is labelled ‘plant-based’ or ‘vegan’ doesn’t make it a healthy option. A vegan diet can technically include anything from lentils to fizzy drinks and biscuits. If you’re leaning heavily on the latter, it could be leaving you short on nutrients and energy.
The evidence we have on the benefits of plant-based diets is actually about whole food plant-based diets, meaning those built around beans, veg, grains, fruit, nuts, and seeds…. not plant-based burgers and vegan cheese.
Processed doesn’t always mean bad, and many processed vegan foods might still be a better option than processed animal products (12), but they can edge out more nutritious options if they become a staple. Over time, this can affect your levels of key nutrients like iron, B12 and omega-3s (13–16), and even influence mood and mental energy (17).
Simple swaps:
Use lentils, chickpeas, mushrooms, tofu or tempeh instead of mock meats
Make your own vegan cheese (e.g. cashews + nutritional yeast + garlic)
Prep snacks at home like oat bars or bliss balls or pick up a simple piece of fruit and a few nuts
Plant-based foods are naturally lower in energy density and higher in fibre, which is great if you’re trying to manage your weight more easily, but it also means you may feel full before you’ve met your energy needs. This can be especially common if you’re coming from a diet higher in animal products. If you’re eating whole plants, you simply need more food to get the same energy.
Quick tips:
Eat little and often if you don’t have a big appetite
Add more calorie-dense foods like nuts, tahini, olive oil, avocados and whole grains
Smoothies are an easy win, include oats, nut butter, chia seeds and fruit for a nourishing energy top-up
See here for more ideas on high energy plant foods.
Even if you’re eating a whole food diet, it’s still important to plan for a few nutrients that may be naturally lower in a vegan diet. These include:
Vitamin B12
Absolutely essential, and not reliably available in plant foods. Deficiency can lead to fatigue, brain fog, and even nerve damage (20).
Take a supplement
Even though the UK RNI is 1.5mcg, we absorb less from supplements, so the doses are higher (23, 24).
Iron
Needed to transport oxygen around the body. Plant iron is called ‘non-haem’ iron, which isn’t absorbed as rapidly as ‘haem’ iron from animals, but with regular plant sources, we can get all the iron we need (26).
Best plant sources:
Pair with vitamin C (like citrus or peppers) to boost absorption (28, 29), and avoid tea or coffee around meals, which can reduce uptake (30).
See here for more on meeting your iron needs on a plant-based diet.
Or visit our shop to download a 4-week high-iron vegan meal plan!
Vitamin C
Vitamin C helps with iron absorption and energy production and although not usually a problem on a whole food vegan diet, if you’re not getting those fruits and vegetables in, you may run low.
Good sources:
Vitamin D
Many people in the UK run low in vitamin D, especially in winter (33). A deficiency can cause fatigue, low mood and muscle weakness (31, 32).
How to get it
Take a daily 10mcg supplement in winter
Choose D2 or vegan D3 (from lichen)
Iodine
Supports thyroid hormones, which regulate metabolism and energy. Deficiency can result in tiredness, weight gain and cold sensitivity (34, 35).
How to meet your needs:
Take a 150µg supplement unless you’re getting it from iodised salt or fortified products
Avoid relying on seaweed because iodine levels are unpredictable and can be a problem at both high and low intakes (36, 37)
Likely not. Any diet, plant-based or otherwise, can lead to fatigue if it’s poorly planned and missing key nutrients. A well-balanced vegan diet can absolutely meet your nutritional needs and help you thrive.
In fact, plant-based eaters often get more fibre, folate, magnesium and antioxidants than omnivores — and there’s no guarantee that people eating meat are hitting their targets for vitamin D or iron either (12).
If you’re still feeling tired after making adjustments, speak to a healthcare professional and consider blood tests for iron, B12, and vitamin D.
Here’s a quick list to run through if you’re feeling low in energy on a vegan diet:
Written by Rosemary Martin RD
Originally researched and authored by Amber Woodhouse RD Feb 2024, updated May 2025.
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