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Dietary Management

People with PWS have a high risk of becoming obese due to the high fat to muscle ratio causing reduced energy expenditure and the need for reduced energy intake, whilst the altered appetite regulation and food reward signalling can make a person obsessive about food and likely to be feeling hungrier than others. Imposing a strict diet on someone with hyperphagia can be difficult, but without effective dietary management, people with PWS will rapidly become morbidly obese and suffer serious health issues that will impact the quality and length of their life.

Understanding nutritional phases in PWS
In the past, PWS was described as a 2 stage syndrome – failure to thrive followed by hyperphagia. It is now known that the changes in appetite and weight gain are more gradual and complex. Parents of children diagnosed in infancy have the opportunity to instil diet modifications and healthy eating habits well before the child’s appetite or interest in food increases. As a result, when phase 3 begins, it is often less severe in families who have implemented early intervention measures.
Phase     Ages                                 Characteristics
1a           0 – 9 months                   Hypotonia with difficulty feeding and decreased appetite
1b           9 – 25 months                 Improved feeding and appetite; growing appropriately
2a           2.1 – 4.5 years                 Weight increasing without appetite increase or excess calories
2b           4.5 – 8 years                    Increased appetite and interest in food, but can feel full
3             8 years – adulthood       Hyperphagic (abnormally increased appetite); rarely feels full
4             adulthood                        Appetite is no longer insatiable (only very few adults)


There is no single, correct way of feeding a person who has Prader-Willi syndrome – different approaches can work for different individuals and families. However, there are several key elements that should be part of any dietary management plan for PWS.

  • As much as possible – eliminate sugar. Brain scans show that sugar is even more rewarding to people with PWS than the rest of us, and families usually find both behaviour and weight management improve when it is eliminated or significantly reduced. Sugar also does very little to curb appetite. Artificial sweeteners should also be avoided. They have fewer calories, but will still have the sweet taste which drives reward, and affect metabolic signals, i.e. the calories the brain associates with sweetness are not received, so it still craves them and hunger is not satisfied.
  • With the help of a dietitian, regularly review your child’s weight and daily nutritional intake and consider whether their energy intake needs to be adjusted. An approximate target amount of calories per day may be recommended (often 50-70% of what is typical for age from phase 2a). Develop a small set of meals and snacks on rotation and become familiar with what the appropriate portion size looks like. Use the same plates or weigh if needed. Focus on fresh vegetables and high quality protein – reduce all processed food and, in particular, processed carbohydrates. Drinks should be water or milk for children. Sweet drinks and artificially sweetened diet drinks should be avoided.

We have detailed resources that cover dietary management, food security and locking options. Request as a hard copy or download here:

  • Aim for at least 30 minutes of exercise per day – more if the person with PWS is overweight.
  • Set up rules and routines around food, such as only eating at the table and set meal times. Decide as a family how you will manage out of the ordinary events such as birthday parties. Consistency is key. Make sure the person with PWS understands that food will only be available at meal times. This may require locking cupboards and fridges.
    These are the principles of ‘Food Security‘ developed by the Pittsburgh Partnership:

A predictable menu sequenced in a predictable routine (focus on sequence rather than time) allows the person to relax and think less about food.

No unplanned extras or opportunities for access to food. Chances to obtain food cause stress. Modify measures as food seeking varies and fluctuates.

The person only has expectations that will be reliably carried out. No other expectations have been raised so there is no disappointment when these are not realised or fulfilled.

Macronutrients Matter

In the past, most families were instructed to follow a low calorie, low fat diet. While calorie control remains important, in recent years the focus has turned to the macronutrient (protein, carbohydrate, fat) balance in the diet. It is now recommended to reduce sugar intake and focus on good quality protein, vegetables, and to include some good fats in the diet. Read food nutrition labels rather than just calorie content and check packaging claims, i.e. ‘no added sugar’ does not mean no natural sugars and ‘low fat’ foods may contain added sugars or sweeteners.

In 2013, Dr Jennifer Miller and her team at the University of Florida published a study that compared a group of children on a calorie controlled diet vs children on a calorie controlled diet that was lower in carbohydrates. They found that children who followed the lower carbohydrate diet weighed less and had less body fat. The recommended diet was:
45% carbohydrate, 30% fat and 25% protein, with at least 20g of fibre per day.

The relative proportions of foods in this diet can be visually represented by the Prader-Willi plate graphic from dietitian Melanie Silverman, and the Prader-Willi food pyramid proposed by Dr Linda Gourash from the Pittsburgh Partnership which places additional focus on gut health by proposing the inclusion of fermented foods. (Note that the red foods in the pyramid are not recommended and should be avoided where possible.)

Prader-Willi Plate

What about very low carb / high fat diets?

Recently there has been interest in the PWS community around very low carbohydrate/ high fat diets – the Modified Atkins and Ketogenic diets. Some families found that energy, behaviour (particularly food seeking) and weight management improved on these diets. In 2016, TREND Community supported ten families to transition to a ketogenic diet and record their experiences in their online database. TREND aims to “turn anecdotes into evidence” as it is very hard to get clinical trials up and running in the rare disease community. The families that lasted for the whole six month trial found it very beneficial and the results are summarised in the White Paper. Research into these diets is still ongoing with several clinical trials underway, but to date, nothing has been published.

Very low carb/ high fat diets will induce ketosis, where the body preferentially burns fats. It is important to have medical supervision from a dietitian and paediatrician who can order and interpret the regular blood tests required. Until the benefits and risk of these diets for PWS have been scientifically determined and any long-term risks considered, we would advise caution.

What about adapting diet for gastro-intestinal issues?

An article published in 2016 has recommended a soft, lower fibre diet for people with PWS. This is contradictory to the high fibre advice normally given for preventing constipation, a common problem in PWS. This new recommendation is a result of new concerns about gastroparesis (slow stomach emptying), bowel obstruction, swallowing dysfunction and high choking risk. If you have concerns about any of the above issues, we would recommend a medical evaluation and dietary adaptation may be advised. To aid digestion, all people with PWS would benefit from regular exercise and drinking water during and between meals to make up for low saliva production. You can also aid digestion by providing more frequent smaller meals and adding probiotic foods to the diet.