Correctional health: Nutrition in prisons


Maintaining nutrition in prisons is an important but difficult aspect to manage. The prison doctor needs to be on the lookout for nutritional deficiencies in the inmate population.

Important concepts to understand in terms of energy expenditure (EE)

Metabolic equivalents (METs): This is an index of EE. A MET is the ratio of the rate of energy expended during an activity to the rate of energy expended at rest. …… (One) MET is the rate while doing nothing. One MET is also equal to an oxygen uptake of 3.5 ml/kg/min

MET-minutes an index of EE that standardises the physical activity output for populations of patients and for different exercises. Number of METS multiplied by minutes gives an indication of exercise volume per week, per day or per month

Kilocalorie (kcal): To convert METs to kcal/min you have to use a persons weight in kg.   kcal is [(METs x 3.5ml/kg/min x kg) ÷ 1000] x 5. kcal is the energy needed to increase the temperature of 1 kg water by 1°C

METs for different activities

20-39yr  40-64yr  >=65yr

Sitting:      1              1                1

Very light <2.4       <2          <1.6

Light         <4.8      <4.0       <3.2

Moderate  4.8-7.2  4-6  3.2-4.8

Vigorous 7.2-10.2 6-8.5 4.8-6.8

Near max >=10.2   >=8.5   >=6.8

If you have 3000 inmates being passive they will utilise 3000 x [(1 x 3.5 x 70 × 24 hours x 60 minutes) ÷ 1000] x5

There is a lot of energy needed just to be inactive. We know that we need inmates to have exercise in order to improve and maintain their health, but any exercise leads to increased MET-minutes per day.

Another formula is the following:

70kg inmate 30 years old (70 x 35 = 2600 kcal per day)

2600 kcal x 4.2 = 10920 kiloJoules per day = 11 megaJoules per day

11 MegaJoules x 3000 inmates = 32760 megaJoules per day

You will frequently see inmates practicing rigourously in the court yards during their 60 minutes exercise breaks. Not every inmate exercises vigourously during those breaks but if they would train one hour per day at 10 METs would translate into:

3000 x 10 METs × 60 minutes would translate into 2 205 000 kcal/ day if the average inmate weighs 70 kg (which indicates how 1 hours vigorous exercise can theoretically be under one quarter of the total 24 hour day’s resting equivalent)

10 METs for 60 minutes is equal to 735 kilocalories, burning 95 gram of fat. 3000 inmates would burn 2 268 000 kilocalories per 60 minute exercise session daily

Nutritional requirements of an inmate population is a major cost driver of a prison. There is therefore a fine balance to be maintained between exercise for health and the prison food budget management

The other factor that will drive up the MET-minutes of the inmate population is the season. Winter season requires more METs to maintain metabolism. Warm bedding and warm clothing can reduce METs used per day.

One other factor that increases MET-minutes increase per day is the increase in the prevalence of “consumption-diseases” such as HIV and tuberculosis. Persons with these diseases have increased metabolic requirements and require more METs.

Inmates work in prison, cleaning, kitchen duties and handyman functions. Increase in work intensity also requires more nutrition for energy

METs Activities

  • 3.3 Sweeping floor
  • 3.0 Cleaning
  • 2.3 Dish washing
  • 2.0 Cooking & food preperation
  • 2.0 Laundry
  • 6.0 Pushing food trolley to units
  • 3.8 Scrubbing floor on hands and knees
  • 4.0 Caring for the sick in prison hospital
  • 3.0 Carpentry
  • 1.0 Watching TV
  • 0.9 Sleeping
  • 5.5 Mowing lawn
  • 4.0 Gardening
  • 1.8 Standing doing arts and crafts
  • 4.0 Bakery
  • 3.0 Throwing out trash
  • 7.0 Jogging
  • 2.0 Dressing
  • 2.0 Grooming
  • 7.0 Casual soccer
  • 5.0 Using crutches
  • 2.0 Walking / strolling

One of the two most problematic prisoner issues that the prison medical services are confronted with on a daily basis is the question of diets and the question of ill-fitting footware. The inmates want to change their diets regularly due to

  • Boredom with current diet
  • Seeing other inmates get “better” diets such as diabetic diets that have more fruits and protein
  • Seeing other inmates get “better” diets such as Moslem diets
  • Developing new diseases which require different diets. An inmate developing tuberculosis or HIV becomes eligible for a high-protein  diet.