Nutritional Supplements for Young Adult Prisoners

Program Theory

Providing nutritional supplements to offenders in a controlled environment, like a prison, is based on the assumption that dietary deficiencies, especially diets lacking in vitamins, minerals, and essential fatty acids, may have negative effects on behavior. Therefore, providing prisoners with nutritional supplements to decrease this deficiency may, in turn, lead to a noticeable reduction in negative, antisocial behavior. The mechanisms underlying potential associations between nutrition and behavior are not yet clearly established, however (Zaalberg et al. 2010).


Essential nutrients, such as vitamins and minerals, have an indirect effect on behavior, because they are connected to changes in neurochemicals in the brain and body, which ultimately influence behavior. For instance, omega-3 fatty acids have been shown in medical research to have important biological roles in cardiovascular health. These fatty acids may, however, also play a critical role in the neurodevelopment of individuals, because they are concentrated in the brain. An omega-3 fatty acid deficiency during important developmental periods, such as prenatal and early childhood, may then increase an individual’s risk for aggressive behaviors later on in life (Hibblen, Ferguson, and Blasbalg 2006).


Target Population

The studies that have so far examined the effects of nutritional supplements on prisoners’ antisocial behavior have included samples of incarcerated juvenile and young adult offenders. This allowed for a controlled environment with a sample of offenders who are prone to aggressive and violent behaviors. Generalizing the effectiveness of supplementing diets with appropriate nutrients on antisocial behavior is currently limited to this population of offenders, however.


Program Components

Providing nutritional supplements is meant to improve nutritional deficiencies among incarcerated inmates. There are currently no set standards for providing nutritional supplements to prisoners, however.


One experiment provided young adult inmates in a British prison with vitamin/mineral supplements as well as supplements of omega-6 and omega-3 essential fatty acids (Gesch et al. 2002). The potency of the vitamins in the supplemental capsules was based on the reference nutrient intake from the United Kingdom, the recommended daily allowance from the European Union, and the daily recommended intake from the United States. There were no standards of daily intake that were used to determine the dosage of the four capsules providing the essential fatty acids. However, a replication study involving Dutch prisoners (Zaalberg et al. 2010) used similar potency of vitamins and minerals from the earlier British study and included a dosage for omega-3 fatty acids based on research from the International Society of the Study of Fatty Acids and Lipids (ISSFAL 2004), research that was not available during the first study.


Prisoners in both studies were provided with supplemental nutrients at lunchtime by prison staff. Lunchtime was chosen to minimize the possible side effects of the supplements, such as nausea and belching.

Intervention ID

18 to 25


Although the original study by Gesch and colleagues (2002) found significant effects on the treatment group that received nutritional supplements, the replication study by Zaalberg and colleagues (2010) found that only one out of the three outcome measures was significantly different between the treatment and control groups, and the effects tended to fade with time.

Study 1

Disciplinary Incidences

The results of the intent-to-treat analysis (which looked at all 231 participants) performed by Gesch and colleagues (2002) found that those in the treatment group who received the active nutritional supplement capsules committed on average 11.8 infringements per 1,000 person-days, a reduction of 26.3 percent compared to the control group, who received placebo capsules. This difference was statistically significant.

A second detailed analysis that only examined the results of 172 participants that were treated a minimum of 2 weeks (90 in the placebo group and 82 in the treatment group) found that the disciplinary infringements for the group receiving active supplements fell significantly compared to the placebo group. The treatment group showed a significant average reduction in disciplinary incidents, from 16 to 10.4 incidents per 1,000 person-days. This represents a 35.1 percent decrease, whereas the placebo group reduced its rate of offending by only 6.7 percent.

When examining the Governor reports, which document the most serious incidents that occur in prison, the treatment group had an average (significant) reduction of 37 percent, whereas the placebo group had a nonsignificant reduction of 10.1 percent. The minor reports, which dealt with less-serious incidents that occur in prison, showed similar results. The treatment group showed a significant reduction of 33.3 percent in minor reports compared to the baseline, while the placebo group showed a small reduction (6.5 percent).

Study 2

Aggression and Hostility

Zaalberg and colleagues (2010) found that the treatment group receiving nutritional supplements reduced their scores on the Aggression Questionnaire by 4.6 points, compared to the placebo group, which reduced its scores by 1.8 points. However, this difference did not reach significance, although there was a (one-tailed) trend (p<.01). Prison staff used the Social Dysfunction and Aggression Scale (SDAS) to rate study participants’ aggression. There was also no significant difference in the development of aggressive and hostile behavior when comparing the SDAS scores of the treatment and placebo groups.

Disciplinary Incidences

Results of the regression analysis showed that the total number of reported incidents in prison was significantly reduced for the treatment group in comparison to the placebo group. When examining proportional differences, the treatment group decreased the number of reported incidents by 34 percent, while the placebo group increased the number of incidents by 14 percent. When incidents involving alcohol- or drug-related violations of prison rules were excluded from the analysis, the results still showed a significant reduction in the number of reported incidents involving prisoners who took supplements as compared to prisoners who received placebos.

Psychological Well-Being

Study participants’ psychological well-being was measured with the General Health Questionnaire–28 (GHQ–28) and the Symptom Checklist–90 (SCL–90). The analysis found no significant differences between the treatment and control groups on the average score of the GHQ–28 and the SCL–90.

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