Acute Responses to Dietary Carbohydrate Manipulation
Condition: Nutrition and Energy Balance
Study type: Interventional

Summary: 
      Sugar is perceived negatively, leading to government taxation and targets to reduce
      consumption. These actions have been taken based on the limited evidence that high-sugar
      diets are associated with greater total energy intake. However, energy intake comprises just
      one half of the energy balance equation (e.g. balance = intake - expenditure). Without
      considering energy expenditure, it is impossible to understand the effects of sugar on
      health. Sugar, and perhaps total carbohydrate intake, may be important for energy balance -
      perhaps by stimulating increased energy expenditure.

      Understanding dietary regulators of energy balance is more important than ever before,
      because diseases like obesity are a consequence of energy surplus (i.e. energy intake >
      energy expenditure). No studies have investigated a causal role of dietary sugar or
      carbohydrate on energy balance. The proposed research will seek to understand the acute (e.g.
      24-hour) responses to manipulating dietary carbohydrate and sugar content on energy balance
      and health.

      This research will contribute to enabling individuals to make informed dietary choices about
      carbohydrate and sugar consumption.

      To achieve this, healthy non-obese adults will be recruited to a randomised crossover study.
      Measures of energy intake, energy expenditure, metabolic health, appetite, food preference,
      and gut microbiota will be taken. All laboratory trials will take place at the University of
      Bath.

      Three diets will be investigated:

        1. Control - reflecting the composition of a typical European diet

        2. Low sugar - the same composition of a typical European diet but with <5% energy intake
           from sugar

        3. Low carbohydrate - low carbohydrate diet with <5% energy intake from sugar and <8%
           energy intake from carbohydrate, replacing carbohydrate energy with fat

      The study will consist of a 3-day lead-in period with the control diet followed by one trial
      day with each diet.
    

Detailed description: 
      Dietary sugar is increasingly perceived in a negative way. This has led to taxation by
      government and guidelines by global public health bodies to reduce sugar intake to <5% of
      energy intake. All available public health guidelines regarding sugar advocate a reduction in
      sugar intake, despite a lack of evidence to support these recommendations. These guidelines
      focus on the association between sugar intake and energy intake, without regard for energy
      expenditure. This oversimplifies situations in which energy surplus is pathological, for
      example in diseases like obesity. This complexity is demonstrated by evidence that dietary
      sugar intake is decreasing in the United Kingdom, whilst rates of obesity have increased in
      the same timeframe.

      It is important to consider energy expenditure in the context of health. The most variable
      component of energy expenditure between individuals is physical activity energy expenditure
      (PAEE), which varies from ~600-2100 kcal per day in men of a similar demographic. Current
      guidelines do not regard the effect that changing dietary sugar might have on PAEE and
      therefore total energy expenditure.

      Carbohydrate availability dictates the capacity to perform physical work. However, the role
      of carbohydrate in regulating physical activity behaviours has only recently been considered.
      Ingestion of a carbohydrate-rich breakfast causes a significant increase in 24-hour PAEE
      compared with no breakfast consumption before midday. The magnitude of this difference is
      greatest prior to midday, near to when carbohydrate had been ingested and when glucose uptake
      to peripheral tissue is increased. This points towards a stimulatory role of carbohydrate or
      sugar on PAEE when carbohydrate is readily available to peripheral tissue. The amount of
      carbohydrate present in skeletal muscle is dictated by the amount of carbohydrate in the
      diet. As physical activity is performed by skeletal muscle, dietary carbohydrate intake may
      regulate physical activity behaviour. Consequently, reducing total carbohydrate intake may
      result in reduced PAEE.

      Studies in which carbohydrate has been manipulated and physical activity has been measured
      have not been sufficient in answering this research question. Often self-report measures of
      physical activity are used, which are not sensitive enough to discern meaningful differences.
      Studies which have measured physical activity objectively, i.e. using pedometers or
      accelerometers, are confounded by a lack of information about actual carbohydrate intake or
      concurrent prescription of exercise interventions. Furthermore, government targets of reduced
      sugar intake to <5% of total energy intake are not aimed at overall carbohydrate intake per
      se. In the breakfast study mentioned, sugar intake was significantly greater amongst
      individuals who ate breakfast compared with individuals who fasted until midday. Therefore,
      it is also plausible that a regulatory role of carbohydrate on PAEE may be due to the type of
      carbohydrate rather than the absolute amount.

      If the availability of carbohydrate to peripheral tissue plays a regulatory role on PAEE,
      then theoretically the effects of manipulating the amount or type of carbohydrate will be
      detectable acutely, within 24 hours.
    

Intervention name(s): Diet
Intervention type(s): Other
Intervention description(s): Macronutrient composition (specifically type and/or amount of carbohydrate) is manipulated
Allocation: Randomized
Intervention model: Crossover Assignment
Masking: None (Open Label)
Primary purpose: Basic Science
Keywords: Nutrition; Carbohydrates