Impact of diet on intestinal metabolism and gut toxicity

There is strong evidence that our diet influences the healthy function of our intestinal tract. Besides the healthy nutrients, some toxins and carcinogens may also be present in the food we eat and additional toxic compounds can be formed or released by intestinal microbiota.

In my research group we look at how carcinogenic compounds are formed in the gut following high consumption of red meat, and how dietary fibre and Vitamin C can prevent their formation.

Furthermore we study mycotoxins, which are toxins produced by some specific moulds growing on agricultural crops. We assess the levels of mycotoxins in foods and human exposure to these dietary toxins.

This work directly benefits consumers by providing evidence on healthy and safe diets.

Research focus

My research interests involve the role of the gut microbiota and microbial metabolites derived from dietary components on the health and function of the intestinal epithelium.

In one project we study the role of gut microbiota in the degradation of masked mycotoxins and the detoxification of mycotoxins. This activity of microbiota is important as it releases additional bound mycotoxins into the large intestine. Furthermore we assess human exposure to mycotoxins using urinary mycotoxin excretion as biomarker in humans.

Another project assesses the effect of diet composition on microbial metabolites derived from carbohydrate and protein metabolism (e.g. butyrate, ammonia, nitrosamines) and their effects on the intestine. In human intervention studies our volunteers consume diets with different levels of carbohydrate, protein and meat and we measure microbial metabolites in human faecal samples.


Research team

Ms Valerie Stevens – Research Assistant

Ms Noshin Daud – PhD student (Elphinstone scholarship)

  • Scottish Government themed programme (2016 – 2021).
  • Early career X-change grant (2016) funded by the Scottish Universities Life Sciences Alliance.
  • Research grant (2014-2015) funded by the Food Standards Agency: Evaluation of masked mycotoxins in foods and their release and uptake in the gut. Joint with the Food and Environmental Research Agency, York, UK.
  • PhD studentship (2013-2016) funded by the Agriculture & Horticulture Development Board: Application of association mapping and genomic sequencing to starch and GI in potato. Joint with The James Hutton Institute, Dundee, UK.
  • EU FP7 collaborative project SATIN - Satiety Innovation (2012 – 2016).
  • Scottish Government themed programme (2011 – 2016).
  • Gratz, SW., Hazim, S., Richardson, AJ., Scobbie, L., Johnstone, AM., Fyfe, C., Holtrop, G., Lobley, GE. & Russell, WR. 'Dietary carbohydrate rather than protein intake drives colonic microbial fermentation during weight loss'. European Journal of Nutrition.
    [Online] DOI: 10.1007/s00394-018-1629-x
  • Gratz, S., Currie, V., Richardson, A., Duncan, G., Holtrop, G., Farquharson, F., Louis, P., Pinton, P. & Oswald, IP. (2018). 'Porcine small and large intestinal microbiota rapidly hydrolyze the masked mycotoxin deoxynivalenol-3-glucoside and release deoxynivalenol in spiked batch cultures in vitro'. Applied and Environmental Microbiology, vol 84, no. 2, 02106-17, pp. 1-9
    [Online] DOI: 10.1128/AEM.02106-17
  • Gratz SW (2017): Invited review: Do plant-bound masked mycotoxins contribute to toxicity? Special Issue: Leading opinions in Toxicology. Toxins 9(3), 85.
  • Gratz, SW., Dinesh, R., Yoshinari, T., Holtrop, G., Richardson, AJ., Duncan, G., MacDonald, S., Lloyd, A. & Farbin, J. 'Masked trichothecene and zearalenone mycotoxins withstand digestion and absorption in the upper GI tract but are efficiently hydrolyzed by human gut microbiota in vitro'. Molecular Nutrition & Food Research, pp. 1-31. DOI:
    [Online] DOI: 10.1002/mnfr.201600680
  • Adam, CL., Gratz, S., Peinado, D., Thomson, LM., Garden, KE., Williams, PA., Richardson, AJ. & Ross, AW. (2016). 'Effects of Dietary Fibre (Pectin) and/or Increased Protein (Casein or Pea) on Satiety, Body Weight, Adiposity and Caecal Fermentation in High Fat Diet-Induced Obese Rats'. PLoS ONE, vol 11, no. 5, e0155871. DOI:
    [Online] DOI: 10.1371/journal.pone.0155871
    [Online] AURA: journal.pone.0155871.PDF
  • Le Leu, RK., Winter, JM., Humphreys, KJ., Young, GP., Christophersen, CT., Hu, Y., Gratz, SW., Miller, RB., Topping, DL., Bird, AR. & Conlon, MA. (2015). 'Butyrylated starch intake can prevent red meat induced O6-methyl-2-deoxyguanosine adducts in human rectal tissue: a randomised clinical trial'. British Journal of Nutrition, vol 114, no. 02, pp. 220-230. DOI:
    [Online] DOI: 10.1017/S0007114515001750
    [Online] AURA: S0007114515001750a.pdf
Additional activities

Science Brief March 2017

Research briefs for the Knowledge Scotland web site

Other Articles

Teaching responsibilities

  • Course coordinator for Foundations of Human Nutrition (PU5015)
  • Lecturing in the MSc Programme Human Nutrition
  • Tutor in Research Skills for Medical Sciences (BSc)

Professional memberships

  • Editorial board member Frontiers in Predictive Toxicity (since 2010)
  • Rowett Internal Ethics Review Panel (Human studies)
  • Athena Swan Self-Assessment Team (Rowett)