Vegetarian High Protein Weight Loss Diets
Condition: Obesity
MeSH terms: Weight Loss
Study type: Interventional

Summary: 
      This study aims to investigate the mechanistic processes involved in protein-induced
      satiety/satiation during weight loss in humans.

      Thsi study will investigate:

        -  How do high-protein weight loss (HPWL) diets rich in meat or soya based protein sources
           impact on profile of 'motivation to eat' both within a day and between days ?

        -  Do biomarkers of satiety alter differentially on meat or soya HPWL diet, as measured by
           monitoring alteration in plasma amino acids and gut-related hormones ?

        -  How does a vegetarian and meat-based weight loss diet impact on nitrosamine excretion in
           faecal samples, as an indicator of faecal toxicity?

      Previous work has indicated that high-protein (30% protein) weight loss diets are more
      satiating (produce less hunger) than normal protein WL diet (15% protein) or a diet
      supplemented with few amino acids. In previous work, a mixed source of protein has been used,
      mainly from meat (beef, chicken, fish). These types of diets have been criticised because of
      the potential negative side effects, including our own work on gut health. It might be that
      alternative vegetable sources of protein could fulfil the diet remit, to be satiating and yet
      still allow weight loss, and maintain a healthy gut.

      Design -within subject, randomised cross-over design after day 3. Each subject acts as their
      own control and will receive each treatment. 18-20 subjects to participate.

      Length of time - Conduct the two nutritional interventions over a period of 14 days, in order
      to reduce effects due to an acute change in nutritional intake.

      PROTOCOL Days 1- 3 - Normal Protein Maintenance diet (NP- MTD, 3 days)

        1. st ARM Days 4-17 - randomised to High Protein-Weight loss-Meat (HP-Soya,14 days),

        2. nd ARM Days 18-31 - randomised to High Protein-Weight loss-Soya (HP-meat,14 days),
    

Detailed description: 
      From literature we know that:

        -  Within-day experiment feeding myco-protein (quorn) versus chicken at lunch resulted in
           an 18% reduction in evening meal ad libitum intake following the quorn meal (Burley, P.
           Blundell, 1993, Eur J Clin Nutr, 409-18).

        -  Feeding casein, soy, pea, wheat gluten, egg albumin, gelatin as part of a mixed meal had
           no influence on post-lunch satiety (Lang et al.,1998, Am J Clin Nutr., 1197-204).

        -  Varying protein source (soy, caseine, gelatin) at breakfast meal at 1.8 and 3.6MJ/meal
           had no impact on 24 hour energy or macronutrient intakes (Lang et al., 1999, Eur J Clin
           Nutr, 959-65).

        -  Comparison of mycoprotein and tofu to a chicken preload before lunch indicated that the
           vegetarian sources were associated with lower food intake at lunch (Williamson et al.,
           2006, Appetite, 41-8).

        -  Addition of 25g protein in a liquid format (whey and soy) led to suppression of food
           intake (pizza meal) 1 hour later, in comparison to water and whey preload.

      It is noted that all of these studies, (i) were conducted over a short time period (within
      day), (ii) none were high-protein weight loss diets (low calorie, high protein), (iii) none
      compared mixed meat versus vegetable source. It is of interest from both a scientific and
      public health point of view whether meat and vegetarian sources of protein similarly impact
      on motivation to eat.

      The diets for this study:

        -  The maintenance diet (MTD) (day 1 - 3) will consist of 15% protein, 30% fat and 55%
           carbohydrate fed to 1.5 x RMR (resting metabolic rate)

        -  The high protein (HP) weight loss diet will be fed to 100% resting metabolic rate (RMR)
           on a 5 day rotation menu, fed as three meals a day, 30% protein, 30% fat and 40%
           carbohydrate; the meat version will be based on chicken and beef meat; the soya version
           based on soya protein or soya-tvp (textured vegetable protein).

      Soya protein is now widely available as milk (ALPRO), margarine (PURE), enhanced bread
      (BURGEN), sausages (GRANOSE), bacon (GRANOSE), burgers (GRANOSE), mince (GRANOSE), powered
      isolate, cheese, cream (SOYA DREAM), yoghurt (ALPRO), chicken-style fillets (GRASSINGTONS).
    

Intervention name(s): High Protein-Weight loss-Soy diet; High Protein-Weight loss-Meat
Intervention type(s): Other; Other
Intervention description(s): • The high protein (HP) weight loss diet will be fed to 100% resting metabolic rate (RMR) on a 5 day rotation menu, fed as three meals a day, 30% protein, 30% fat and 40% carbohydrate; the soya version based on soya protein or soya-tvp (textured vegetable protein).; • The high protein (HP) weight loss diet will be fed to 100% resting metabolic rate (RMR) on a 5 day rotation menu, fed as three meals a day, 30% protein, 30% fat and 40% carbohydrate; the meat version will be based on chicken and beef meat.
Other intervention name(s): SOY HP WL diet; MEAT HP WL diet
Allocation: Randomized
Intervention model: Crossover Assignment
Masking: None (Open Label)
Keywords: weight loss; high protein diet; plant protein; satiety; soy