Research support

Soy versus Meat-based Weight Loss Diets

grant holder
Prof. Dr. Alexandra Johnstone
- University of Aberdeen, Rowett Institute of Nutrition and Health

Hunger and appetite responses were compared in 20 healthy, obese men consuming a high soy protein weight loss diet versus a meat based high-protein weight loss diet.


  • Previous work has indicated that high-protein (30% of diet as protein) meat-based weight loss diets are highly satiating, and reduce the free food intake over a four-week period (1,2).
  • There is limited data on assessing the effect of different types of protein on appetite in weight loss studies (3). Previously, a mixed meat source of protein was used in our high protein diets, but this approach has been criticised both from a policy and public health perspective because of potential negative side effects, especially on gut health (4).
  • There is acceptance that plant based weight loss diet may offer protection from diseases (5).
  • It may be that alternative plant-based sources of protein could be satiating, and yet maintain a healthy gut during weight loss, and we set up a study to test this, using soy protein

Research undertaken: a human dietary intervention study investigating protein induced satiety during weight loss, using soy protein.

We compared hunger and appetite responses in 20 healthy, obese men eating a vegetarian high-protein weight loss diet and a meat based high-protein weight loss diet. All meals were provided as 30% protein, 30% fat and 40% carbohydrate from energy, to provide basal energy requirements. Appetite bio-markers like plasma amino acid profile and gut hormones were monitored in response to a test meal challenge which reflects the impact of the diet on volunteers’ satiety. (

Main findings and concluding remarks

  • Over the two weeks, subjects lost similar amounts of weight, on average 2.41 and 2.27 kg on the vegetarian high-protein weight loss and meat based high-protein weight loss diets respectively, with similar reduction in fat-mass and preservation of fat-free mass, due to the high protein component.
  • The vegetarian high-protein weight loss had a similar impact on appetite and motivation to eat as the meat based high-protein weight loss diet.
  • Blood biomarkers improved with weight loss for both high protein diets (plasma cholesterol, low density lipoproteins (LDL), high density lipoproteins (HDL), triglycerides and glucose)
  • There was a greater reduction in total cholesterol with the plant based diet for cholesterol and LDL cholesterol. This finding could be attributed to the composition of soy-based meals, (i.e. fibre, phytochemicals, and other micro- and macronutrients).
  • Since appetite control and weight loss was similar in both weight loss diets, plant-based high-protein diet could be a healthier alternative to meat based high-protein weight loss diets, achieving desired results without any negative health effects (e.g. risk of colonic disease).


Neascu M, Fyfe C, Horgan G, Johnstone AM. Appetite control and biomarkers of satiety with vegetarian (soy) and meat-based high-protein diets for weight loss in obese men: a randomized crossover trial. Am J Clin. Nutr. 2014 Jun 18; 100(2):548-558.



  1. Westerterp-Plantenga MS, et al. Annu Rev Nutr 2009; 29:21-41.
  2. Johnstone AM, et al. Am J Clin Nutr 2008; 87(1):44-55.
  3. Due A, et al. Int J Obes Rel Metab Disord 2004; 28(10):1283-90.
  4. Russell WR, et al.. Am J Clin Nutr 2011; 93(5):1062-1072.
  5. Clifton P. Brit J Nutr 2012; 108:122–129.