Do you need more protein if you eat little meat?
Eating little meat does not automatically mean taking in less protein, but the quality of plant protein is lower. Pay attention to your sources, combine them wisely, and from age 65 onwards it is definitely worth giving protein quality some extra thought.
People who eat little or no meat generally do not take in less protein than meat eaters. Vegan, vegetarian, and semi-vegetarian diets all deliver a total protein intake of between 10% and 17.4% of daily energy. So the total amount need not be the problem.
What does differ is the make-up of that protein. Vegans get 77 to 98% of their protein from plant sources. Plant protein contains, on average, fewer of the building blocks your body needs most, and is absorbed slightly less well than animal protein. People who eat exclusively plant-based foods are therefore well advised to pay close attention to quality: combine legumes, grains, and nuts throughout the day, because together they supply all the essential building blocks.
In older adults (aged 65 and over) this point matters more. Plant-based eating may be less than ideal for maintaining muscle mass at an older age, but this has not yet been expressed in concrete numbers. A study looking into this in people aged 65 and over is currently under way; results are not yet available.
For young, active people, a well-planned plant-based diet does not appear to harm sports performance. There are even early indications of benefits on certain measures of endurance and strength, although that evidence is limited.
One point that is separate from protein but still worth mentioning: deficiencies in vitamin B12, the omega-3 fatty acids DHA and EPA, and iron are more common on plant-based diets. These deficiencies can be avoided with targeted supplementation and careful planning, but should not be ignored. For children and young people, extra vigilance is called for: whether a strict vegan diet covers all growth needs cannot yet be stated with certainty on the basis of current research.
This answer is based on a large comparative study of protein intake across different diet groups, a published study protocol for research in older adults (results not yet available), a review of studies in young athletes, and two reviews on nutritional deficiencies and plant-based diets in children. The evidence on total protein intake is reasonably solid; the evidence on muscle mass in older adults and performance in athletes is preliminary.
Do you get enough essential amino acids on a purely plant-based diet?
A plant-based diet delivers all essential amino acids, as long as you eat enough total protein and keep your meals varied. For active people, a minimum of 1.2 grams of protein per kilogram of body weight per day is a sound starting point.
Why do you build less muscle when you do a lot of endurance sport?
Research shows that you can build muscle mass just fine on a combined schedule. If you also want to maximise explosive power, it helps to train strength before endurance and to spread your sessions out.
Do you live longer by eating less protein, or more?
The ideal protein level differs by stage of life: in middle age less appears to be better, while after the age of 65 getting enough protein is protective. What is clear: choose plant-based protein sources as much as possible and limit processed red meat.
Does extra protein help with losing weight without losing muscle?
Extra protein while losing weight helps: you lose slightly more fat and keep on average around 0.4 kg more muscle mass than on a normal-protein diet. Combine it with strength training for the best result.