Scientists from the University of Iowa have discovered a natural compound (Ursolic Acid) that increases muscle mass.

The Pembrokeshire proverb, written by John Pavin Phillips in 1866, “Eat an apple on going to bed, And you’ll keep the doctor from earning his bread.” A very simple principle to live by. At the same time, it was a claim with no scientific foundation. Well over a century later, there exists substantial evidence to support his philosophy.

Apples (or pure apple juice) are one of the most common fruits consumed as part of a balanced diet and to contribute towards our “5 a day”. They come in a number of different types from the relatively mild Gala apple, to the sweet Pink Lady and even the slightly sour Granny Smiths variety. They all however include the natural compound ursolic acid which is found in abundance just under the skin (don’t discard the peel).

Health benefits

Amongst other fruits, apples are known to have wide-ranging medicinal benefits. Research suggests that apples, cloudy apple juice and apple-based products possess biological activities which translate into health benefits, guarding against cardiovascular disease, asthma, pulmonary dysfunction, diabetes, obesity and even cancer. Phenolic compounds such as quercetin and epicatechin in particular are known to reduce the risk of cancer, have a strong anti-oxidant effect and can also act as anti-inflammatories. Apples also have a low glycemic index (GI) rating, meaning the sugar present is released slowly into the blood, perfect for an early morning snack.

	Apples	Apple Juice
Water (g)	85.3	88.1
Energy (kcal/kJ)	54/227	48/203
Protein (g)	0.3	0.07
Fat (g)	0.6
Carbohydrate (g)	11.4	11.1
Fibre (g)	2	0.77
Potassium (mg)	144	144116
Calcium (mg)	7	4.2
Magnesium (mg)	6	6.9
Phosphorus (mg)	12	7
Vitamin C (mg)	12	1.4
Organic Fruit Acids (g)	0.5	0.74

Table 1. Average nutrient content in apples and apple juice (per 100g).

Scientists have now highlighted a compound called ursolic acid that reduces skeletal muscle atrophy. Ursolic acid is the major waxy component in apple peels and is also present in many other edible plants.

Skeletal muscle atrophy is a gradual wasting of muscle characteristic of a low protein diet, physical inactivity, starvation and is also a common consequence of aging. It can also impact on the immune system, complicating several diseases such as cancer, HIV / AIDS and chronic respiratory diseases amongst others.

The first experiment conducted targeted fasting-induced muscle atrophy (no food was permitted for 24 hours) to mimic the effects of malnutrition. They found that mice administered with ursolic acid in a fasted state, had more muscle bulk in their hind limbs in comparison to those mice that were just fasted.

A second group of fully-fed mice had two lower hind limb muscles (gastrocnemius and tibialis anterior) denervated (nerve supply cut) meaning that the mice could no longer use/contract the muscle but the muscle still received a normal nutrient flow. This imitates a period of inactivity similar to injury or a sedentary, non-exercising lifestyle. The mice supplemented with ursolic acid saw a reduction in denervation-induced muscle atrophy. This suggests that supplementing your diet with ursolic acid when injured reduces the rate at which muscle mass is lost.

Most strikingly, when ursolic acid was administered in an unstressed condition, i.e. the mice were healthy, had full access to food and the ability to roam freely, it actually induced muscular hypertrophy (an increase in muscle mass). The mice exhibited larger, heavier skeletal muscles, larger skeletal muscle fibres and increased grip strength.

Figure 1. The first schematic (left) highlights the greater proportion of larger fibre diameters in the rats supplemented with ursolic acid. The second schematic (right) demonstrates the more powerful grip strength exhibited in the rats ingesting ursolic acid.

This would indicate an overall increase in body mass, however there was no significant differences in body weight before or after administration. This suggests that ursolic acid can even reduce fat content (adiposity).

Unfortunately, as the study set out to identify a method of reducing muscle atrophy, they did not go on to investigate the effects ursolic acid has when exposed to an exercise regimen. Furthermore, these findings are based on data collected from mice and to what extent they apply to humans remains unclear.

Sporting applications

Ursolic acid could become a wonder supplement. In terms of injury alone it could reduce the amount of time an athlete is out injured, meaning athletes miss fewer meetings or games, aiding consistency and improving form as well as their respective teams getting more out of their players.

For example, if a goalkeeper suffers a fracture of the wrist, hand or finger, the volume of work they can do with said arm is severely limited, leading to a local reduction in strength and conditioning (they can still run, maintaining their cardiovascular fitness). Potentially, ursolic acid could be given to help reduce the amount of muscle mass lost in the arm during the recovery period, leading to a smaller amount of time until they are deemed “fully fit” once again.

From an ethical perspective, should ursolic acid have the same effects on humans as in mice it brings into question whether high doses of the compound would be considered legal. It is likely that a systematic search would also occur leading to derivatives that may be more difficult to trace, more potent or more efficacious. Currently the 2012 WADA prohibited list does not mention the substance underlining the early stages of its development.

Eating one apple may help to keep the doctor away, but in the not so distant future eating many may invite the anti-doping authorities to take a closer look.