Research comparing diets heavy, light and free of meat has found vegetarianism is cheaper, healthier and easier on the environment.

But dietitians urge caution with the study, produced by the manufacturer Sanitarium, which is owned by the Seventh-Day Adventist Church.

They argue that going meat-free is not necessarily better.

The findings show it costs $508 a week to feed four adults on a traditional meat diet. A reduced meat diet costs $418 a week, while a vegetarian diet costs $394.

''A massive 20 per cent reduction in costs can be achieved by maintaining the vegetarian diet,'' the company said in a statement.

The analysis also showed the plant-based diet used 50 per cent less water, led to 12 times less land being cleared and created a six times lower level of greenhouse gas emissions than a meat-rich diet.

It also contained almost 50 per cent lower saturated fat and 25 per cent more fibre and folate.

But weight-loss analyst Dr Manny Noakes said while vegetarian diets could be beneficial they could also be unhealthy.

''We have to be careful about painting all vegetarian diets with the same healthy brush because there are many things like doughnuts, for instance that are very unhealthy but could be part of such a diet,'' Dr Noakes said. AAP