A Randomised Controlled Trial Assessing The Impact Of An Intermittent Energy Restricted Diet On Weight Loss, Insulin Sensitivity and Heart Rate Variability In Men and Women With Central Obesity

Prediabetes rates in England have showed a marked increase, more than tripling between 2003 and 2011. It is characterised by an impaired fasting glucose or impaired glucose tolerance that increases the risk of progression to type 2 diabetes (T2D). It has been estimated that approximately 90% of T2D is attributed to excess weight. Central obesity is a primary driver of increased cardiometabolic risk due to its lipotoxicity effects, promoting a proinflammatory state that facilitates insulin resistance and beta cell dysfunction. A high waist circumference measurement, indicative of central obesity, is associated with increased risk of cardiovascular diseases and T2D, and is a stronger predictor of T2D than BMI. BMI has limitations as an indicator of adiposity since it doesn't distinguish lean from fat mass, and does not indicate body fat distribution. Conventionally, continuous energy restriction (CER) diets have been used for weight loss, which consist of a constant daily energy deficit relative to total energy expenditure. The impact on weight loss and health of an intermittent energy restriction (IER) approach has only rarely been investigated (although the "5:2 diet" has been popularised in lifestyle books aimed at the general public). An IER diet consists of a predefined period of time severely restricting energy intake, alternated with a period of greater energy intake. This approach was shown to confer metabolic benefits in overweight and obese women at risk of breast cancer with baseline BMI of 2445 (Harvie et al., 2013; Harvie et al., 2011).

Rationale: An IER diet using meal replacements (VLCD foodpacks used as total dietary replacements for 2 consecutive days each week, and a food-based energy-restricted diet for the other 5 days of the week) may modify cardio-metabolic disease risk factors compared to an energy-matched CER diet.

Research question: In centrally obese subjects, assessed by a high waist circumference measurement, does adherence to an IER diet have enhanced cardio-metabolic benefits compared to a CER diet? Hypothesis: Increases in insulin sensitivity following a 4 week dietary intervention with an IER weight loss programme will be greater compared to a standard CER programme.

Objectives:

1. A randomised controlled parallel design trial will determine the impact of a short-term IER diet compared to a CER diet on primary outcome variables (insulin sensitivity) in healthy subjects with a high waist circumference.
2. To assess the impact of an IER diet on secondary outcome variables, including body composition, heart rate variability (HRV, a measure of cardiac autonomic function, including parasympathetic and sympathetic activity), blood pressure, vascular function, other markers of insulin resistance, inflammation/adipokines, plasma lipid profile, plasma norepinephrine, ketosis, the gut microbiome and cognitive function in healthy subjects with a high waist circumference.