IMD WATCH
SPORT AND PKU Sarah Adam Metabolic Dietitian Royal Hospital for Children. Queen Elizabeth Hospital Sarah provides the dietetic support to adults with IMD at the Royal Hospital for Children, Queen Elizabeth Hospital. She also works with the metabolic paediatric dietitians and gets involved with infants and children too. She attained a post graduate certificate in Sports Nutrition from Coventry University in 2012.
Sarah Howe Specialist Dietitian Sarah is an experienced NHS Dietitian specialising in the area of Inherited Metabolic Disorders.
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Sport’s nutrition is becoming increasingly recognised by the general population, by those who either participate in sport and exercise to enhance their athletic performance, or who simply want to improve their physique. This article takes a look at how PKU is managed to support and enhance the sport and exercise experience. Social media is full of toned bodies and picture-perfect meals with carefully calculated macros and, with well-known athletes promoting their nutrition regimes; so much so that it is often hard to decide what diet is best to follow and if and when you need to change your diet when you exercise. This is no different for people living with Phenylketonuria (PKU), an inherited disorder of the metabolism of the essential amino acid, phenylalanine (Phe). The challenge for people with PKU is to control their blood Phe within tight parameters by adhering to a diet severely restricted in natural protein and supplementing it with a Phe-free amino acid substitute. This typically provides 60g protein equivalent for adults to meet the majority, if not all, of their protein requirements and usually contains the full complement of vitamins and minerals. Energy needs are mostly met with the use of specially manufactured low protein foods, such as bread, milk, flour and pasta prescribed by their GP, and fruits and vegetables that are allowed without careful measurement. It is not a diet of convenience and it requires a certain level of skill for cooking and food preparation, as well as organisation, to follow it successfully. The goal of nutrition for sport is about meeting the nutritional demands specific to the chosen sport, by supporting the metabolic and physical
adaptations to that type of exercise. In turn, this can enhance athletic ability, reduce the risk of injury and illness through appropriate recovery nutrition strategies, tailored to the goals of the individual athlete. Dietitians specialising in inherited metabolic disorders are often asked for dietetic advice by adults with PKU regarding how or whether their diet for PKU can be incorporated into their physical training. Questions patients often ask include: “Will sport affect my Phe control?”; “How can I build muscle on a low protein diet?”; “How can I best recover after exercise?”. Presently, there is limited evidence on the effect of exercise on blood Phe concentration in PKU patients. Two studies have shown that acute exercise did not change blood Phe concentration in PKU patients.11,12 However, more studies are needed in larger numbers of patients, as well as controlling for dietary intake and the type of exercise to confirm results. There is evidence in the PKU population that women in particular are vulnerable to weight gain.4 A recent study concluded that a low protein PKU meal had a reduced thermic effect of feeding and reduced postprandial fat oxidation, speculating that this could be contributing to obesity.1 Exercise can enhance fat oxidation and should be encouraged in PKU. www.NHDmag.com October 2018 - Issue 138
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IMD WATCH DIETARY ASSESSMENT
To help answer these questions and to determine nutritional needs, there are many factors to consider in the dietetic assessment in relation to exercise. This includes the individual’s own sporting objectives, their anthropometry, body composition and nutritional objectives, the training program they follow to determine their level of fitness and activity and, of course, their current dietary intake. Nutritional requirements can then be determined and compared against the current intake in order to help identify the main dietary issues that need to be addressed and negotiated. A key guideline which may be referred to regarding meeting the nutritional and fluid needs of physically active adults and athletes, is the Joint Position Statement by the The Academy of Nutrition and Dietetics and Dietitians of Canada on Nutrition and Athletic Performance.8 HOW CAN I BUILD MUSCLE ON A LOW PROTEIN DIET?
Protein is essential for tissue repair and muscle protein synthesis (MPS) in response to physical exercise, as well as for general body protein turnover. There is little evidence in the scientific literature on muscle building and sports nutrition specific to those on a low protein diet for PKU. However, what is known about the metabolic and physical response to exercise and nutrition can at present be applied to individuals on a low protein diet. To support muscle growth and the physical adaptations to exercise, overall it is important to consume both sufficient protein and calories. Most exercising individuals will typically require 1.2-2.0g of protein/kg body weight/day.8 An adult with PKU on diet requires 0.8g protein/ kg/d plus 40% to account for the digestibility of amino acids and the effect of amino acids on Phe control.10 This equates to 1.12g protein/kg/d for sedentary adults with PKU. Exercise and protein both stimulate MPS and are synergistic when protein is consumed before or after exercise. The timing of protein consumption appears to be most effective for muscle growth when consumed within 30 minutes to two hours after exercise and at regular three- to four-hourly intervals across the
day.7,2 Furthermore, MPS is enhanced for at least 24 hours after resistance, sprint and endurance exercise, plus the muscle becomes more receptive to protein consumed over this period of time.3,8 However, the effect of protein timing in relation to exercise is perhaps lessened for those who are already consuming sufficient amounts of protein (e.g. 1.6g/kg/d).5 The optimal dose of protein to consume immediately after exercise is 15-20g (or approximately 10g of EAA).7-9,2 The protein substitutes for PKU typically contain 20g of protein equivalent, of which 10g is essential amino acids (EAA), making these substitutes ideal for supporting muscle growth. Older adults and those wishing to maintain muscle mass and restrict energy intake may benefit from higher doses of 30-40g.5 For a person with PKU, these recommendations could be achieved by consuming one 20g protein equivalent substitute at each mealtime, with one immediately after finishing the training session. Studies looking at pre-sleep protein consumption show that consuming protein after an evening training session improves the nitrogen protein balance.13 This may be of particular relevance to individuals with PKU, as the highest Phe level is the morning sample after the overnight fast. The natural protein from the food exchanges can be divided between the three main meals or in a pre- or post-exercise snack. The PKU protein substitute is also a rich source of branched chain amino acids. In particular, leucine can independently drive protein synthesis, although sustained effects are seen when combined with EAA.6 For example, an 80kg athlete would need 1.2-2.0g of protein/ kg body weight/day. This equates to 96g-160g/ day of total protein. If they required a low protein diet for PKU and their daily allowance for natural protein is 6g (six exchanges) to control their blood Phe, then they would need 5 x 20g Phe-free protein substitute to meet the remainder of their protein requirements. In total, 106g/day of protein (1.32g protein/kg/d) would be consumed: 100g from the protein substitute and 6g from the protein exchange foods. Due to the restrictive nature of the PKU diet, most protein substitutes contain the complete range of vitamins and minerals, the provision www.NHDmag.com October 2018 - Issue 138
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LIFE WITH PKU DON’T LET ANYTHING STOP YOU This information is intended for Healthcare Professionals only. The PKU Lophlex range are Foods for Special Medical Purposes used in the dietary management of PKU and must be used under medical supervision of a Healthcare Professional.
IMD WATCH Table 1: Suitable isotonic drinks for PKU Sports Drink
Carbohydrate %
Sodium (mmol/l)
Powerade Cherry
4%
12
Gatorade Tropical Burst, Cool Blue, Orange
6%
18
Lucozade Sport Mango and Passion Fruit, Brazilian Guava
6.5%
21.7
of which should be considered for those with particularly high protein requirements to avoid excessive intakes. Powdered tablets and capsule protein substitutes free of micronutrients could be used to supplement protein only. HOW CAN I IMPROVE MY RECOVERY FROM EXERCISE?
A good recovery is important, as it helps the athlete train harder and ultimately leads to improved performance in competition. The goals of recovery are to: • refuel energy (muscle glycogen) stores and rehydrate; • promote muscle repair and growth; • promote physiological adaptation to training; • support immune function. An effective and quick recovery is particularly important when participating in repeated high intensity, strenuous, or highly skilled training sessions multiple times a day, or in close succession. Individuals involved in fitness activities three to four times a week, for 30 to 60 minutes at a time, will not require additional carbohydrate; recovery needs can often be met from usual meals, protein substitute and snacks, including appropriate amounts of complex carbohydrate foods such as low protein pasta, rice or bread. Some protein substitutes contain 20-30g of carbohydrate per dose. Glycogen is the key fuel for exercising muscles and its stores in the muscle are limited depending on the exercise intensity and duration. The availability of carbohydrate to the muscles is important, as it will influence performance, so glycogen stores should be optimal prior to exercise. Glycogen stores are maximised by consuming a high carbohydrate diet, 8-12g/ kg/d depending on the level of fitness, volume and intensity of training.8. Prolonged exercise over 60 minutes of moderate to high intensity 46
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exercise will deplete glycogen stores, so dietary strategies to offset this are required. For example, consumption of a 6-8% carbohydrate containing fluid, consumed at regular intervals and/or snacks with a high glycaemic index to deliver 30g-60g carbohydrate per hour, can be employed. Isotonic sports drinks typically contain 4-8% carbohydrate and 10-20mmol/l sodium. The taste is designed to encourage drinking, supplement glucose and reduce the risk of hyponatraemia if consumed in large quantities, due to the addition of electrolytes. For PKU, fluids need to be free of aspartame, so labels need to be checked. See Table 1 for suitable isotonic drinks for PKU. Speedy refuelling requires consuming appropriate amounts of fluid, carbohydrate and protein immediately, to within at least two hours of finishing exercise. Furthermore, taking protein and carbohydrate together during the recovery period can improve the overall body protein balance after exercise8 and minimise increases in muscle damage. CONCLUSION
Exercise is safe for those with PKU in regards to their metabolic control and should be encouraged for its health benefits. Individuals with PKU participating in general recreational exercise where the goal is simply to keep fit and be a healthy weight, can support their activities by consuming regular meals based on complex low protein carbohydrate to optimise their glycogen fuel stores and by taking their protein substitutes at timely intervals across the day and immediately post exercise for muscle repair and growth. For those exercising at higher volumes and intensities, the diet for PKU can be tailored to meet the nutritional demands of the sport. However, further research on this subject is required to underpin guidance.