In the 1990s, when I became vegan, it was a common phenomenon to see very skinny vegan guys. Nowadays this is less common (in Europe), and I think the reason is mostly that (1) vegan food is much more widely available and (2) higher-protein convenient vegan food (soya milk, tofu, tempeh, etc.) is much more widely available. The reason why so many, especially young vegan guys (less so girls) were so skinny is that they ate less often and they ate a relatively low-protein diet.
Even though I speak of this problem - being much skinnier than you would like to be - as if it were a problem of the past, it is still highly prevalent: again, especially among young vegan men (let's say 17 to 20 years old). And probably it's more common among in countries where - as I wrote above - convenient higher-protein vegan foods are less frequently available.
Note: if you want to lose weight, you're in the wrong place. Look here instead.
Picture of vegan burger stolen from Black Cat Hackney
First: what's a healthy body weight?
There are two ways to look at body weight: from a societal view of "beauty standards" (in some countries "fat is beautiful") and from a medical (health) view.
I am not going to discuss the societal norms about body weight here. But this is what the medical view on body weight is:
Body weight is categorized into four (or more) categories based on the so-called body mass index (BMI).
- BMI <18.5: underweight
- BMI 18.5 - 24.9: ideal weight
- BMI 25 - 29.9: overweight (but not yet obese)
- BMI 30 or higher (obese, i.e. very overweight)
You can calculate your own BMI based on your body weight (in kilograms) and your body height (in metres). You can just use this calculator to calculate your BMI, or you can calculate your BMI yourself in this way:
"your body weight" (in kg) / "your body height" (in metres) ...
... and then divide this number once again by "your body height" (in metres).
Note: if you are of East Asian decent (Chinese, Japanese, South East Asian, etc.), your ideal BMI should probably not be higher than 24.
Note: if you are a bodybuilder or other strength athlete with very high muscle mass, then the BMI will categorize you as overweight, even though you may not have excessive amounts of body fat. That means the BMI categories are not really adequate for bodybuilders and strength athletes with very high muscle mass.
Why gain weight?
You may want to gain weight because of societal expectations or because of your own expectations. However, from a health perspective too, it is not ideal at all to be underweight. Being underweight weakens your bones (increasing the risk for bone fractures) and weakens your immune system (increasing your risk for all kinds of infections, including potentially dangerous infectious diseases which could kill you). Underweight is associated with an increased risk of premature mortality (early death).
What is body weight?
Which body tissues make up the bulk of your body weight? Three are especially important to mention: adipose tissue (= body fat), bones, and muscle tissue (on your legs, torso, arms). Being underweight means that your body fat will be low - but also your muscle mass will be low (atrophied), and your bone mass will also be lower (thinner and weaker bones).
Which weight gain do you want?
Obviously, not all weight gain is healthy or desirable. If you excessively gain body fat, that isn't healthy and your body will look chubby but not muscular. If you are skinny, you want to gain weight in the form of muscle mass. Some added body fat usually comes along with this (which is fine), and your bone mass will also increase. But mostly this means focusing on gaining muscle mass.
Note: to stimulate muscle gain, it's useful not just to provide enough building material (protein) for your body but to also stimulate your muscles with exercise. You can use your body weight exercises (push-ups, pull-ups, sit-ups, squats, for example - just doing a few of these every other day will have a visible effect). We're not talking about massive bodybuilding here. We're talking about achieving a healthy body weight.
5 steps to eat well and gain weight
1) Eat more protein
This is probably the most important aspect. Especially if legumes are not a regularly eaten food where you live, it is very easy to end up with a vegan diet that is based on grains, vegetables, fruit - with only small amounts of legumes. This would be a diet that is quite low in protein. Even though grains also contain relatively large amounts of protein, they are usually low in the essential amino acid lysine. Legumes on the other hand are rich in lysine but have less of the essential amino acid methionine. If you eat grains and legumes together (let's say a ratio of 50% grains and 50% legumes - very roughly), then you will have a "complete" protein, i.e. a protein source that is both relatively high in protein content as well as relatively high in all the essential amino acids that your body needs to build and maintain muscle mass. (Really, we do not have a dietary requirement for protein but rather for the essential amino acids, which are the building blocks of protein). You do not necessarily have to combine grains and legumes within the same meal (within a day or two is OK) - but combining them both within the same meal is very common (beans and rice, bread and peanut butter, seitan and tofu, pasta and tofu, lentils and rice, etc.) and makes meals more satisfying, too.
Note: so-called pseudograins, including quinoa, amaranth, buckwheat, millet, etc., are higher in lysine than "real" grains like wheat, barley, oats, etc.
Note: whole grains are higher in protein than refined grains (white rice, white bread, white flour, etc.).
Note: depending on where you live (in many countries), you may have access to vegan meat alternatives (burgers, sausages, etc.). These are very often based on soya or pea protein or wheat protein or a combination of these, meaning they are usually high in protein (which is good). But they may also be high in salt (which is less good because in large amounts it can harm your arteries in the long term). Some meat alternatives are NOT high in protein, for example if they are made from green jackfruit.
Note: similarly, while soya milk is typically high in protein, this is not the case for most other plant-based dairy milk alternatives (including almond milk, oat milk, rice milk, etc.). Usually the protein content is stated on the packaging.
2) Eat more frequently
If you often skip meals, then eat more often: bodybuilders eat very frequently. That means they eat around 5 or 6 meals a day (roughly and typically). They do this to constantly provide calories and protein and stimulate weight gain in the form of muscle growth. If you often skip meals - this may be because when you're at a friend's house, or visiting family, or somewhere around town, or traveling, or at a school/workplace cafeteria, it may be that vegan food isn't really available at all, or just small snacks (rather than full meals), or only vegetables, or only other types of low-protein and/or low-calorie options. So, basically do not skip meals and eat additional snacks - at least temporarily. Make sure to chew well or blend foods and to easy into "new" foods (that your body is not used to yet) by starting with small portions. This way you can mostly avoid digestive discomfort (like bloating or even diarrhoea).
3) Eat enough fat!
If you're underweight, do not eat a low-fat diet. That does not mean that you should replace high-protein foods (legumes) with fat. But eating high-fat foods like healthy oils, coconut, nuts, seeds, nut butters (peanut butter etc.), or seed butter (tahini etc.) to your diet will add calories, and nuts and seeds will also provide some additional protein. Apart from this, nuts (almonds, cashews, pecans, walnuts, hazelnuts, ...) and seeds (ground sesame seeds, tahini, pumpkin seeds, sunflower seeds, ...) are very good for your health in general. So, it's worth recommending eating a handful or two of nuts/seeds per day.
Note: nuts and seeds should be chewed well or ground. For example, if you eat whole sesame seeds, many if not most of them will not be chewed up properly and they will just pass through your entire digestive tract intact (undigested), and you will not obtain any calories or nutrients from them. Only what your body absorbs provides nutrients.
4) Drink some calories.
But do not replace higher-protein meals with low-protein drinks! If you just want to add more calories to your diet, you can do so by drinking beverages that have calories (unlike water or plain tea or coffee which have no calories). Calories come from fat, alcohol, starch, and sugar (and protein). So, examples of beverages that provide calories are: fruit juices, sugar-sweetened beverages (Coca Cola etc.), alcoholic drinks (beer, wine, and all other alcoholic drinks), soya milk, sugar cane juice (if you live somewhere in the tropics) etc. However, not all of these (like Coca Cola etc.) are healthy. Be sure to understand that point 1 ("Eat more protein") is the first priority. Drinking caloric beverages while not getting enough protein can make you chubby (your body fat and body weight will go up), but your muscles will not grow. Nevertheless, if you are struggling to consume enough calories, drinking calories can be useful because if your body is in a state of "calorie deficit", your body will "burn up" some of the protein you eat as calories instead of using this protein to build and maintain muscle mass.
Note: smoothies are drinks too. Blend up some fruit and soya milk. You can also add spices, avocado, nut butter, and/or a bit of oil.
5) Make sure your food is tasty!
If you cook for yourself, add something SWEET (a bit of juice/sugar), something SOUR (some lemon or vinegar), something SALTY (a little soya sauce/salt/seaweed), something FATTY (ground nuts/nut butter/olive oil or canola oil/some grated coconut) & something BITTER (most vegetables are a tiny bit bitter – so you do not have to add anything). Also use ingredients that will add the flavour UMAMI (for example tomato sauce, vinegar, nutritional yeast, yeast flakes, mushrooms, sea vegetables, olives, sauerkraut, soya sauce or other fermented foods). In addition, add lots of spices and/or herbs and use less salt.
Note: while I would recommend that you centre your diet around healthy food groups: legumes, fruits, vegetables, whole grains, nuts, and seeds, you do not have to be a purist about it. If you are generally healthy, it's totally fine to consume some less healthy food (often labelled "junk food" etc.) such as fried or deep-fried foods, candy bars, etc.
6) In the long term: make sure you are getting enough of all micronutrients!
Micronutrients are vitamins and minerals, and it's quite easy to fall short of some of these on a vegan diet in the long term. It is also just as easy to get enough of all of these nutrients on a vegan diet - but only if you include good source of these nutrients in your diet, of course (and take a supplement for vitamin B12). You can see the ten nutrients that require most attention on a vegan diet here in this overview. One of the nutrients on this list is iodine, and iodine is very relevant for body weight. This is because iodine is important for your thyroid gland (in the front of your neck). If your body ends up with a relatively severe iodine deficiency or just the opposite, iodine excess, then this can throw your thyroid gland out of control and cause thyroid "overdrive" (hyperthyroidism - you'll lose a lot of weight) or thyroid "underdrive" (hypothyroidism - you'll gain a lot of weight but in a bad, unhealthy way). If you have just started out on a vegan diet, and you don't want to familiarize yourself with all of these nutrients and foods that are good sources for these nutrients (what is mentioned in the overview), then I would recommend taking a general multivitamin & multimineral supplement in the short term. Not all multivitamin/multimineral supplements are vegan-friendly (watch out for gelatine capsules, especially), but many are. In the long term (many years) I would recommend avoiding taking supplements of nutrients you don't need (especially iron). General multivitamin/multimineral supplements also have the advantage that they are widely available and that they usually contain nutrients in moderate amounts (about the daily recommended intake, usually) rather than very high amounts (which are common in some supplements and which can be bad).