Abstract
Objective: Since short-term weight loss is often achievable in overweight individuals but long-term weight maintenance is generally poor, this thesis examines the effect of the nature of support programmes and macronutrient composition on weight maintenance following weight loss.
Research design and methods: A 2x2 multifactorial design was used to compare two support programmes and two diets differing in macronutrient composition on maintenance of weight loss over a 2-year period. Two hundred women who had recently lost at least 5% of initial body weight were randomised into one of two support programmes. One provided intensive expert, health professional support with regular circuit training classes. The other provided brief and frequent 'weigh-ins' and support facilitated by a nurse. Participants were also randomised with regard to recommended diet composition. One eating plan was high in carbohydrate and dietary fibre, emphasising low glycemic index foods. The second eating plan was relatively high in monounsaturated fat and protein and had a low overall glycaemic load. At baseline, 1 and 2-years, weight, waist circumference and blood pressure were measured and body composition was estimated using bioelectrical impedance. Three-day weighed diet records were collected to estimate dietary intake. A fasting blood sample was used to measure glucose, insulin and lipids.
Results: At 2-years weight was measured for 87% of participants. On average those randomised to the Expert Support Programme reduced weight by 2.5kg while those on the Nurse Support Programme reduced weight by 3.6kg (difference between support programmes, P=0.976). On the High Carbohydrate Diet average weight loss was 2.4kg compared with a loss of 3.8kg on the High Monounsaturated fat Diet (difference between diets, P=0.419).
At follow-up, there were no significant differences between the support programmes with regards to body composition, systolic and diastolic blood pressures, blood lipid levels, glucose, insulin, and predicted insulin sensitivity. From a health system perspective and relative to the Nurse Support Programme, the Expert Support Programme cost $NZ 928, 970 per QALY gained (or $9, 290 per person).
At follow-up, there were no significant differences between the dietary prescriptions with regard to body composition, systolic and diastolic blood pressures, triglycerides, HDL-cholesterol, glucose, insulin and predicted insulin sensitivity. However, total and LDL cholesterol were significantly lower on the High Carbohydrate Diet compared with the High Monounsaturated fat Diet (total cholesterol 0.2mmol/l, P=0.044, LDL cholesterol 0.2mmol/l, P=0.042). At follow-up those on the High Monounsaturated fat Diet reported significantly higher intakes of saturated fat (1.5%TE), total fat (5%TE), monounsaturated fat (2.4%), and a significantly lower intake of carbohydrate (-5%TE) than those on the High Carbohydrate Diet.
Conclusion: A relatively inexpensive nurse led programme appears to be as effective as a more costly expert health professional led programme in achieving weight maintenance over a 2-year period. This inexpensive and successful weight maintenance programme offers a feasible option for implementation in primary health care in New Zealand. Similarly, both dietary approaches produced comparable beneficial effects in terms of weight loss maintenance. However the High Carbohydrate Diet was associated with lower levels of total and LDL cholesterol, possibly due to a lower intake of saturated fat.