Diabetes mellitus is a group of metabolic disorders resulting from defects in insulin secretion, insulin action (sensitivity) or both, which cause abnormalities in carbohydrate (CHO), protein and fat metabolism that can be life threatening, if untreated. There are many types of diabetes—each a distinct clinical entity with different complication risk profiles and management requirements.
Acute complications of diabetes include hyperglycaemia, which can induce dehydration, ketosis and electrolyte abnormalities, weight loss and blurred vision; and hypoglycaemia, when on insulin, or sulphonylureas, which can induce a coma. Long-term complications (e.g. cardiovascular disease, renal failure, loss of vision, amputation) in suboptimally managed diabetes are irreversible with a high morbidity and mortality. Short- and long-term treatment goals include maintenance of blood glucose levels (BGLs) within an optimal range and prevention of the onset and progression of long-term complications.
People with diabetes can become elite athletes and train and compete at a high level of exercise intensity and endurance. Several renowned athletes with diabetes—including Sir Steven Redgrave, who won five successive gold medals in rowing from 1985 to 2000; a US professional cycling team (Team Novo Nordisk), who all had type 1 diabetes; and Wasim Akram, the Pakistani fast bowler—provide testament to the ability to overcome perceived barriers of having diabetes. However, for athletes with diabetes on insulin, matching insulin dosage with glucose use during exercise and CHO intake to maintain optimal BGLs can be challenging.
This chapter focuses on clinical practice and nutrition guidelines for athletes with diabetes, particularly those on insulin who participate in different types and levels of intensity of physical activity. CHO and protein recommendations for athletes with diabetes before, during and after exercise are similar as for athletes without diabetes but may need adjustment. The metabolic response to exercise is influenced by BGLs and circulating insulin prior to starting exercise. Regular self-monitoring of BGLs, especially around exercise, as well as ongoing consultation with a team of clinicians—including a dietitian with experience in diabetes management, a diabetes educator and a physician—is essential to assist the athlete with diabetes to fine-tune insulin dosage and match energy and CHO requirements.
CATEGORIES OF DIABETES MELLITUS
Most cases of diabetes fall into two broad categories: type 1 and type 2. However, there are other types of diabetes involving genetic defects of the pancreatic beta cells, genetic defects in insulin action and endocrinopathies, as indicated in Table 20.1. Diabetes can also occur during pregnancy (i.e. gestational diabetes) and as a consequence of other diseases or trauma to the pancreas (e.g. injury, inflammation, alcohol misuse and drug- or chemical-induced). Type 1 diabetes is not reversible but other types may be transient, depending on the type, cause and success of intervention. The World Health Organization provides details of recently updated classifications and diagnostic criteria for different types of diabetes and pre-diabetes (www.who.int/health-topics/diabetes).