A summary of evidence about the effect of diet and exercise on anti-social behaviour in prison.
Exercise and physical activity has many physiological and psychological benefits. Most evidence is about the general population. But there is a growing interest about their effect on prisoners. What effect might exercise have on prisoners’ well-being, custodial behaviour and future offending?
There is also growing evidence that diet affects not only our health, but our cognitive ability and behaviour too. What do we know about diet and prison behaviour? Might food or supplements potentially help manage or prevent aggression and violence?
What do we know?
Does diet affect thinking and behaviour and can changes to diet improve prison behaviour?
There is fairly strong evidence linking a Mediterranean or healthy diet with lower risk of depression. There is some evidence to suggest links between low blood glucose levels and irritability and aggression.
There is early, promising evidence around essential Omega-3 and -6 fatty acids. This suggests a diet or dietary supplements of these may reduce aggression and violent behaviour in prison. There is no good quality research examining any link between diet and reoffending.
Can physical activity and exercise improve prison behaviour, and reduce reoffending?
Exercise can reduce depression and anxiety in prisoners, perhaps as a coping mechanism. There is some evidence to suggest that physical activity:
- may reduce levels of aggression
- can be used to maintain and promote order and control across the prison
- can provide skills that have the potential to aid desistance (desistance is how people with a previous pattern of offending abstain from crime) - however, more evidence is needed to assess the impact exercise can have on reoffending
How does diet affect thinking and behaviour?
Diet not only affects health, but cognitive ability and behaviour too. Systematic reviews conclude that:
- iron supplements improve attention and concentration in adolescents and women - they may improve IQ among those with iron deficiency
- lower vitamin D levels are associated with poorer cognitive performance and an increased risk of Alzheimer’s Disease
- however, we don’t know whether increasing vitamin D levels improve performance or reduced risk of dementia There is good evidence that:
- a Mediterranean diet, (rich in oily fish and seed oils, providing Omega-3 and -6 essential fatty acids) reduces risk of depression and cognitive impairment
- a ‘healthy’ diet, rich in fruit and vegetables, fish and whole grains, is associated with a lower risk of depression
Evidence suggests (but is not conclusive) that:
- deficiencies in Omega-3 and -6 essential fatty acids may be linked to suicide, violence and aggression
- supplements can reduce aggression in healthy adults, children, the elderly and people with a psychiatric diagnosis
- there is some association between low blood glucose levels, and irritability and violent behaviour
How does diet affect prison behaviour?
A good quality study1 examined the effect of nutritional supplements on antisocial behaviour, in an English Young Offenders Institution. This found that those who took supplements committed 26.3% fewer infringements of prison rules compared to a control group. While this is impressive, it is a single study, in one site, so we can have only limited confidence in this finding.
A Dutch study 2 found no impact from supplements on self-reported aggression or prison staff perceptions. However, there was a significant impact on reported incidents of aggressive and rule-breaking behaviour. The group taking supplements saw a 34% drop in number of reported incidents pre- to post-trial. Those taking placebos had a 14% increase in reported incidents over that time. Prisoners were not told which type of pill they were taking. But by the end of the experiment the majority could guess whether they were given supplements or placebos. Similar findings were also reported with children aged 13-17, in juvenile detention.
We are not aware of any studies examining the link between diet and reoffending.
How does exercise affect behaviour and mood?
Evidence suggests that Physical activity can impact on depression, anxiety, stress and anger levels in the wider community. Physical changes result from exercise like reduced body temperature and release of dopamine. These can produce calming effects and improved mood. The overall impact of exercise on mood is uncertain. Exercise is however, moderately more effective at reducing depressive symptoms than no treatment or anti-depressants. Neuroscience suggests a link between physical activity and anti-social behaviour3.
How does exercise affect the mood and behaviour of prisoners?
Several studies indicate that physical activity reduces depression, anxiety and hopelessness. The strength of the studies varies. Some show that any exercise has the potential to improve depression and anxiety and act as a coping mechanism. There is less evidence on the relationship between physical activity and behaviour in prison. There is some promising evidence of a link. Some studies suggest exercise alleviates boredom and allows prisoners to ‘burn off some steam’. This could have a calming effect and limit disruptive, aggressive behaviour.
In a qualitative study staff reported that exercise can be used:
- to maintain order and control by teaching prisoners about discipline
- to channel aggression or frustrations, and
- as an incentive for positive behaviour
Sport was also cited as a way of:
- managing violence
- providing opportunities for prisoners to learn how to manage their emotions, and
- breaking down barriers by promoting positive social interactions, group working and cohesion
We need more evidence about whether certain physical activities have a greater impact on mood and behaviour.
How does exercise affect offending and desistance?
Some studies suggest exercise programmes can help develop skills and opportunities for education or employment on release. However, despite strong arguments, there is limited evidence on the effect of exercise on reoffending and desistance. More research is needed to determine any impact of sport on reoffending.
A Sporting Chance: An independent review into the role of sport in the justice system highlights the role that sport and physical activity can play in rehabilitation and reducing reoffending, identifies best practice from across the custodial estate and makes recommendations for enhancing provision. (MoJ 2018)
Gesch, C. B., Hammond, S. M., Hampson, S. E., Eves, A., & Crowder, M. J. (2002). Influence of supplementary vitamins, minerals and essential fatty acids on the antisocial behaviour of young adult prisoners: Randomised, placebo-controlled trial British Journal of Psychiatry, 181, 22-28.
Zaalberg, A., Nijman, H., Bulten, E. et al., (2010). Effects of nutritional supplements on aggression, rule-breaking and psychopathology among young adult prisoners Aggressive Behavior, 26, 117126.
Jackson, D.B., and Beaver, K, M. The Impact of Physical Exercise on Anti-social Behaviour: A Neurocognitive Perspective.
This page summarises the available evidence base and is informed by independent academic peer review. It does not represent Ministry of Justice or Government policy.