Question: I'm vegan and in general I don't have any problem maintaining my weight, but for the last few months I've wanted to increase my weight and it's been really hard. 

Could others who have had the same problem give me some tips or advice on how to gain weight on a vegan diet?

Answer: 
If you want to gain lean weight - instead of a mix between lean weight and fat -, then you need a high protein diet. Researchers don't seem to agree on exact numbers, but, for adults undergoing regular weight training, [most aim at higher than 1g/lb of bodyweight](http://www.bodybuilding.com/fun/maki1.htm) (2.2g/kg for those under the metric system). 

So, not only you need to ingest more calories than your TDEE ([estimate yours here](https://www.supertracker.usda.gov/bwp/index.html)) to keep on gaining weight, but you also need to keep a high protein ratio, as well.

The best sources for piling up protein in a vegan diet are soy protein (usually 20-24g of protein per 30 grams), wheat gluten (70-75g per 100 grams) and spirulina algae (arguably 10-20g per 30 grams). Other sources might include peanut butter, other nuts and beans, but bear in mind most of those sources have low protein ratios. 

Of course, changes in your diet should be discussed with your dietitian. Exercise is also an important factor, since high protein diets have been proven not to provide additional benefits for sedentary adults.
I would like to answer this question both for vegetarians and vegans from the Ayurvedic viewpoint (the only difference being vegans do not take dairy).

Ayurveda is a system of well-being and medicine that originates in India, and it recommends a vegetarian diet. According to Ayurveda, one can gain weight by eating *vegetarian food that is grounding, warm, oily, smooth, stabilizing, and substantive.* Other factors like a regular daily schedule and a light exercise routine are also involved.

It is recommened to eat three heavy meals at the same time everyday.

You can read more at this [article](https://www.banyanbotanicals.com/info/ayurvedic-living/living-ayurveda/health-guides/weight-management-guide/an-ayurvedic-approach-to-gaining-weight/):

> 
> ...You will want to orient your diet around healthy, whole foods that are
>  deeply nutritious. Choose foods that are warm, moist, oily, grounding,
>  nourishing, smooth, and stabilizing, over foods that are cold, dry,
>  light, or rough. Favor the sweet, sour, and salty tastes over the
>  pungent, bitter, and astringent tastes. Build your meals around staple
>  foods that naturally taste sweet, such as fruits, grains, root
>  vegetables, milk, ghee, fresh yogurt, eggs, nuts, seeds, and
>  vata-pacifying meats. Nourishing and rejuvenating dishes such as Sweet
>  Potato Halva and Urad Dal (Split Black Gram) are fantastic, as are substantive soups and
>  stews. You can also include grounding, nutritive snacks in between
>  meals. For instance, fill a jar with dates, pour warm
>  Ghee (clarified butter) over them and let the ghee solidify. Eat one or two of these ghee
>  dates in the early morning or any time between meals for a
>  rejuvenative boost of energy. Other supportive snacks include soaked
>  and peeled almonds, soaked cashews, and date shakes.
>  Experiment with what works for you and keep snacks handy so that you
>  can reach for quality nourishment rather than a quick fix of empty
>  energy (i.e., sugar or junk food).
> 
> 
> 

This [page](https://www.banyanbotanicals.com/info/ayurvedic-living/living-ayurveda/diet/vata-pacifying-foods) gives a list of fruit, vegetables, grains, legumes etc to be preferred and avoided for weight gain.