According to scientists at the Karolinska Institutet in Sweden, a compound found naturally in spinach may have a powerful effect on muscle strength.
The study found that mice supplied with 'nitrate' in their drinking water developed significantly stronger muscles, than those who were not.
"From a nutritional perspective our study is interesting because the amount of nitrate that affected muscle strength in mice was relatively low," said Dr Andrés Hernández, researcher at the Department of Physiology and Pharmacology in a statement.
"Translated to humans it means that we can obtain the equivalent volume by eating more of a vegetarian diet, as nitrate is found naturally in several leafy vegetables, especially in beetroot juice, for example. There are currently no dietary supplements containing nitrate."
According to a statement, the researchers located that the 'nitrate mice' had a higher concentration of two different proteins in their muscles.
These two proteins, CASQ1 and DHPR, are involved in the homeostasis of calcium, a critical determinant of muscle contraction.
Future research will concentrate on how such a link could be explored further and practically applied to aid people with muscle weakness.
Spread peanut butter on wholemeal toast or crackers as a protein-rich snack. Peanuts are an excellent source of protein, with one tablespoon containing about four grams of protein.
A half cup of cottage cheese contains around 16 grams of protein, yet only has 102 calories and two grams of fat, as opposed to other cheese, where the protein benefits are counteracted by the high fat content. If you're not too keen on the cheesy taste, add a handful of berries or fruit to the bowl, or spread it on a wholemeal cracker for a savoury snack.
Egg white contains four grams of protein and is cholesterol-free. Whip up an egg white omelette for your lunch or some scrambled egg sandwiches for a tasty way to boost your protein intake.
Tuna fish is a great source of protein, with one tin can containing 25 grams of protein. Snack on it straight from the tin if you like it enough, or mix it with sweetcorn and a tiny bit of low-fat mayonaise to make a spread that you can have with pitta bread or crackers.
Although lentils can taste a little bland on their own, they can be easily added to your lunchtime salad or into a hearty homemade soup. Lentils are a great source of protein and an easy way to boost your protein levels. One cup of lentils equals to around 18 grams of protein.
A single cup of quinoa contains around 18g of protein and it can be easily added to homemade granola bars or cookies if you fancied a sweeter snack.
Beans contain a high level of protein and can be eaten in all different ways. Why not make a bean dip by blending different types together mixed with a little bit of olive oil? Or add them to a homemade soup and sprinkle them on your lunchtime salad.
A handful of raw, unsalted nuts, like almonds, hazelnuts, walnuts are great snacks to keep handy throughout the day. You only need a small handful for your daily allowance on these, but they are high in fiber, protein, and "good" fats.