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Nuts & Gut Health

What impact do nuts have on the gut microbiome?

Our body is closely tied to the community of bacteria that lives in our intestine – the gut microbiome. For some time, we assumed gut bacteria is only needed to help keep the colon healthy but this exciting new area of study is uncovering how gut bacteria impacts inflammation and chronic disease such as obesity. So many foods impact on the amount and diversity of bacteria and interestingly for us nuts are one of those foods.

What is the gut microbiome?

A large US study, The Human Microbiome Project, has uncovered that more than 90% of the gut microbiome is made up of two types of bacteria - Firmicutes and Bacteroidetes bacteria, with the rest from Actinobacteria, and Proteobacteria(1) but only a fraction have been cultured and their functions analysed. It’s estimated the gut is colonised by more than 100 trillion microorganisms.(1)

Microbiome diversity increases from birth, peaking in early adulthood but declines with age(2). These different bacteria have a range of functions, including nutrient release and absorption, protection against pathogens, and changes to the immune system(3). Further research is needed though to determine how our age, gender, genetics, BMI, health status, diet, mode of delivery, geographic location, and medical treatments/antibiotics alter the type and amount of bacteria present in our intestines.(4-6)

What impact do nuts have on the gut microbiome?

This is a fascinating new area of research for nuts but it is still in its infancy. Nuts are foods (prebiotics) for the bacteria (probiotics) and nut skins in particular, appear to play an important role since they are rich in fibre and phytochemical compounds, with antioxidant and anti-inflammatory properties.(7)

Both raw almonds and roasted almonds appear to increase the growth of gut bacteria.(8) Raw almonds have been found to stimulate the growth of bifidobacteria and Eubacterium rectal bacteria leading to increased butyrate production (9) - a short chain fatty acid which is thought to keep colon cells healthy. A study involving 48 healthy adults, eating either 56g of roasted almonds or 10g of almond skins a day for six weeks, resulted in significant increases in Bifidobacterium and Lactobacillus bacteria in faecal samples.(10) An almond and pistachio study also saw increased bacterial growth.(11).

Different types of fibres have been identified in hazelnut skins and in time may also show prebiotic potential.(12)

Chestnut extracts and chestnut flour appear to protect probiotics enabling them to survive stomach acids and bile making it to the large intestine intact(14). Attempts have been made to make a chestnut based “yoghurt”(15).

It is early days yet but we know nuts are highly nutritious foods that do not lead to weight gain and this impact on the gut microbiome may be just another way they help control weight.

Research has found those of us colonised with Faecalibacterium, Bifidobacterium and Lactobacillus bacteria have significantly less risk of developing obesity-related diseases such as type 2 diabetes and cardiovascular disease.(16-18) These species are able to produce high levels of lactate, propionate and butyrate short chain fatty acids(17) which are thought to impact on inflammation. Inflammation is though to impact on insulin resistance which leads to weight gain.

Interestingly animal and human studies have found the Bacteroidetes/Firmicutes ratio is decreased in those who are obese compared to healthy weight individuals.(17-20) Gut bacterial changes in obese mice increase intestinal permeability, resulting in intestinal and adipose (body fat) tissue inflammation which could also lead to weight gain.(21)

There is so much left unanswered but this new area of study offers promising results. Until such time, healthy diets need to be high in fibre and include fruits, vegetables, legumes, wholegrains, fermented dairy, other fermented foods and of course nuts, to provide sources of pre-and probiotics to positively affect the gut microbiome.

1) Human Microbiome Project, C .Structure, function and diversity of the healthy human microbiome. Nature 2012;486:207–214.
2) Belizário JE, Napolitano M.. Human microbiomes and their roles in dysbiosis, common diseases, and novel therapeutic approaches. Front Microbiol. 2015;Oct 6;6:1050.
3) Brown,C.T et al. Genome resolved analysis of a premature infant gut microbial community reveals a Varibaculum cambriense genome and a shift towards fermentation-based metabolism during the third week of life. Microbiome 2012;1:30.
4) Arumugam, M et al. Enterotypes of the human gut microbiome. Nature 2011;473: 174–180.
5) Koren,O et al. A guide to enterotypes across the human body: meta-analysis of microbial community structures in human microbiome datasets. PLoS Comput. Biol. 2013;9:e1002863.
6) Clemente,J.C et al. The impact of the gut microbiota on human health: an integrative view. Cell 2012;148:1258–1270.
7) Mandalari G, Faulks RM, Bisignano C, Waldron KW, Narbad A, Wickham MS. In vitro evaluation of the prebiotic properties of almond skins (Amygdalus communis L.). FEMS Microbiol Lett. 2010 Mar;304(2):116-22.
8) Liu Z et al In vitro and in vivo evaluation of the prebiotic effect of raw and roasted almonds (Prunus amygdalus). J Sci Food Agric. 2016 Mar;96(5):1836-43.
9) Mandalari G, Nueno-Palop C, Bisignano G, Wickham MS, Narbad A. Potential prebiotic properties of almond (Amygdalus communis L.) seeds. Appl Environ Microbiol. 2008 Jul;74(14):4264-70.
10) Liu Z, Lin X, Huang G, Zhang W, Rao P, Ni L. Prebiotic effects of almonds and almond skins on intestinal microbiota in healthy adult humans. Anaerobe. 2014 Apr;26:1-6.
11) Ukhanova M, Wang X, Baer DJ, Novotny JA, Fredborg M, Mai V. Effects of almond and pistachio consumption on gut microbiota composition in a randomised cross-over human feeding study.Br J Nutr. 2014 Jun 28;111(12):2146-52.
12) Montella R, Coïsson JD, Travaglia F, Locatelli M, Bordiga M, Meyrand M, Barile D, Arlorio M. Identification and characterisation of water and alkali soluble oligosaccharides from hazelnut skin (Corylus avellana L.). Food Chem. 2013 Oct 15;140(4):717-25.
13) Arena A, Bisignano C, Stassi G, Filocamo A, Mandalari G. Almond Skin Inhibits HSV-2 Replication in Peripheral Blood Mononuclear Cells by Modulating the Cytokine Network. Molecules. 2015 May 15;20(5):8816-22.
14) Blaiotta G, La Gatta B, Di Capua M, Di Luccia A, Coppola R, Aponte M. Effect of chestnut extract and chestnut fiber on viability of potential probiotic Lactobacillus strains under gastrointestinal tract conditions. Food Microbiol. 2013 Dec;36(2):161-9.
15) Blaiotta G1, Di Capua M, Coppola R, Aponte M. Production of fermented chestnut purees by lactic acid bacteria. Int J Food Microbiol. 2012 Sep 3;158(3):195-202.
16) Kootte,R.S et al. The therapeutic potential of manipulating gut microbiota in obesity and type2 diabetes mellitus. DiabetesObes.Metab. 2012;14:112–120.
17) Ley,R.E et al. Microbial ecology: human gut microbes associated with obesity. Nature 2006; 444,1022–1023.
18) Le Chatelier,E et al. Richness of human gut microbiome correlates with metabolic markers. Nature 2013;500:541–546.
19) Ley,R.E et al. Obesity alters gut microbial ecology. Proc.Natl.Acad.Sci.U.S.A. 2005;102:11070–11075.
20) Verdam,F.J et al. Human intestinal microbiota composition is associated with local and systemic inflammation in obesity. Obesity(SilverSpring) 2013;21:E607–E615.
21) Cani,P.D et al. Selective increases of bifidobacteria in gut microflora improve high-fat-diet-induced diabetes in mice through a mechanism associated with endotoxaemia. Diabetologia 2007;50, 2374–2383.

Published 15th April 2016

This article is based on an article Lisa Yates wrote for Medical Observer - a GP magazine.

Do nuts cause gallstones or kidney stones?

There have been two population based studies investigating the relation of frequent nut consumption and the risk of gallstones (1,2).

Men consuming five or more 30g serves of nuts per week had a significantly lower risk of gallstone disease (30% risk reduction) than men who never ate or who ate less than one serve per month(1).

Data from the Nurses' Health Study (2) showed that for women, frequent nut consumers (≥5 times/wk) had a 25% reduced risk of needing cholecystectomy (removal of the gallbladder) than women who never ate nuts or who ate less than one serve a month.

These outcomes remained true despite the type or content of fat in the diet(1,2). Thus, it appears that the frequency of nut consumption is equally protective of gallstone disease in both sexes.

There is less evidence for the role of nuts in reducing the risk of kidney stones. Consumption of a DASH style diet - which is rich in fruit, vegetables, legumes, nuts and wholegrains; moderate in low fat dairy products; and low in sweetened beverages, salt and processed meat is associated with a 40% reduced risk of kidney stones(3).

1)Tsai CJ et al. A prospective cohort study of nut consumption and the risk of gallstone disease in men. Am J Epidemiol. 2004 Nov 15;160(10):961-8.
2) Tsai CJ et al. Frequent nut consumption and decreased risk of cholecystectomy in women. Am J Clin Nutr. 2004 Jul;80(1):76-81.
3) Taylor EN et al. DASH-style diet associates with reduced risk for kidney stones.J Am Soc Nephrol. 2009 Oct;20(10):2253-9.

Last updated July 2016

Should people with Diverticular Disease eat nuts?

There’s no good evidence that avoiding nuts is helpful for people with diverticular disease – in fact it may even be counterproductive. Nuts are a valuable source of fibre in a high-fibre diet for diverticular disease.

1) Weisberger L, Jamieson B. Clinical inquiries: How can you help prevent a recurrence of diverticulitis? J Fam Pract 2009;58(7):381-2.
2) Strate LL et al. Nut, Corn, and Popcorn Consumption and the Incidence of Diverticular Disease. JAMA 2008;300(8):907-914.

Last Update September 2016

Are nuts gluten free/ can people with Coeliac Disease eat nuts?

Raw and roasted nuts are gluten free, and can be enjoyed by those with Coeliac disease, provided they don’t have any other flavourings added. Always check the ingredients list for any gluten containing additives such as thickeners or maltodextrins. In fact many gluten-free recipes make use of ground nuts instead of grain flours. Nut meals that include nut skins can provide extra fibre. Check out our gluten-free recipes - they are marked 'GF' in the title.

Last Update September 2016

Are nuts gluten free?

Raw and roasted nuts are gluten free provided they don’t have any other flavourings added. Always check the ingredients list for any gluten containing additives such as thickeners or maltodextrins. Nut meals such as almond, hazelnut and chestnut meals are a great alternative to gluten based flours. Adding nuts to a gluten free diet can also help boost the nutrient content of the diet, particularly fibre.

Check out our recipe section - those recipes marked 'GF' are gluten free.

Last update September 2016