Adolescence is a period of rapid growth and development, characterised by major changes in body size, including increased muscle development. Increasing fruit and vegetable (FV) consumption during childhood is widely encouraged as part of a healthy diet. Epidemiological evidence suggests that FV consumption and/or intakes of nutrients associated with a FV-rich diet may play a role in improving muscle strength and power^(1-3). However, the evidence is still inconclusive and the majority of studies to date have been conducted in older adults. The importance of FV intake for muscle function during adolescence has rarely been examined. We therefore carried out a cross-sectional study to examine the association between FV consumption and muscle strength and power in an adolescent population.

The Northern Ireland (NI) Young Hearts Project

The results are based on data collected from approximately 2000 boys and girls, aged 12 and 15 years, who participated in The Young Hearts (YH) 2000 Project (1999 – 2001). YH2000 is the second in a series of large cross-sectional studies carried out in NI schoolchildren, the primary aim being to examine the status of modifiable coronary risk factors during adolescence⁴. During the study, dietary intake, including total FV consumption, was assessed using a 7-d diet history. Grip strength and maximal vertical jump power (as proxy measures of muscle strength and power, respectively) were measured with a hand-held dynamometer and Jump-MD meter, respectively. Associations between FV intake and muscle strength and power were examined using linear regression analyses.

Higher FV consumption was positively associated with muscle power

The study revealed that muscle power was significantly higher in boys and girls who consumed high intakes of FV (>237.71 g/d and >267.57 g/d respectively) versus low intakes (<135.09 g/d and <147.43 g/d, respectively), after adjusting for confounding factors including age, BMI (z score), pubertal status, energy intake, physical activity and socio-economic status. No such associations were evident between increased FV consumption and muscle strength in either boys or girls. Similar associations were observed when FV were analysed separately.

Comparison with previous studies

Associations between FV intake and muscle strength and power have been observed previously, although the evidence mainly comes from cross-sectional studies in older adults. These studies found that low serum carotenoid status, which may reflect low FV intake, was associated with poor muscle strength and other measures of physical performance^(1-3).

Through what mechanism does FV act on muscle?

A number of possible mechanisms have been suggested for the association between FV and muscle. The high antioxidant content of FV may offer protection against oxidative stress and inflammation within muscle cells. The alkaline salts present within FV may also act as a buffer against excess acid. Another potential mechanism, worthy of further investigation, is the influence of nitrates present within FV which may help improve muscle contraction by improving mitochondrial efficiency within the muscle cells⁵.

In summary:

• Increasing FV consumption during adolescence should be encouraged as a potential means of improving muscle power
  
• In this cohort of adolescents, there was no independent association between increased FV consumption and muscle strength
  
• Intervention studies are required to determine whether muscle strength and power during adolescence can be improved through increased FV consumption