Lectins and health - a review

Have you heard of lectins? They are a type of protein found in small amounts in over 30% of plant foods including grains and legumes. While they are not well known, popular fad diets including the Paleolithic diet (Paleo diet) cite lectins as a main reason to exclude grains and legumes from the diet. As the topic of lectins is making headlines in the Paleo world, GLNC has reviewed the science on the role of lectins and lectin containing foods within a balanced diet. 

Background

The Paleo diet is an eating plan which is intended to closely reflect that of our hunter gather ancestors – GLNC’s Position Statement on the Paleo Diet can be found here. A quick Google search on lectins, directs you to the websites, and blogs of prominent Paleo’s (avid Paleo dieters)  from around the world. Paleo’s describe lectins as toxic and destructive anti-nutrients which damage the intestine, cause a leaky gut leading to obesity  and diseases ^{(1, 2)}. The presence of lectins in grains and legumes is one factor which underpins the Paleo recommendation to exclude these foods. However, examination of the scientific evidence as a whole indicates there are flaws in this argument.

The science doesn’t stack up

The beliefs which underpin the avoidance of lectin containing grains and legumes are based on studies which have limited generalisability to humans. The studies used to support the argument against lectins were mostly conducted in animals, using doses of purified lectins which could not be achieved through foods alone and some studies even injected the lectins directly into the bloodstream.^(3-13) In the studies which observed negative effects in humans, they involved people with pre-existing intestinal damage and/or the participants of the study ate foods which were not adequately prepared for human consumption i.e. unsoaked legumes.^{(14, 15)}

It is inaccurate and misleading to apply the results of such studies to humans, let alone use them to support the dietary recommendations for large populations. Upon reviewing the broader science on lectins, including a comprehensive review of the literature published last month, there is no convincing evidence to indicate that lectins cause harm. The claims made by proponents of paleo diets to avoid grains and legumes due to these foods continaing lectins are not supported by the scientific eveidence. ^{(3, 16)}

Interestingly, there is some evidence that low doses of dietary lectins, consumed within adequately prepared foods may in fact have health benefits including anti-cancer effects and assist weight management by helping to promote a feeling of fullness. ^{(17, 18)}

Grains and legumes promote health

In contrast to claims to avoid grains and legumes, there is a significant body of evidence, including large population studies (in humans) which indicate that higher intakes of grains, mostly whole grain and high fibre are associated with improved nutrition and a reduced risk of a disease ^{(19, 20)} – including cardiovascular disease, obesity, type 2 diabetes and certain cancers. Comprehensive reviews of scientific trials also demonstrate legumes have beneficial effects on the markers of chronic disease such as blood pressure, cholesterol levels and blood glucose control.^(21-23)

Grains and legumes provide a range of essential nutrients including carbohydrates, protein, vitamins, minerals as well as dietary fibre and phytonutrients. In support of the Australia Dietary Guidelines and in line with the evidence on the nutrition and health effects of grains and legumes, the Grains and Legumes Nutrition Council (GLNC) recommends that Australians should enjoy grain foods 3 – 4 times a day, choosing at least half as whole grain or high fibre grain foods, and enjoy legumes at least 2 – 3 times each week. 

To view the complete scientific topic summary prepared by GLNC contact GLNC via email: contactus@glnc.org.au or phone: 1300 GRAINS

References: 

1. Sisson M. The Lowdown On Lectins 2013 [January 2014]. Available from: http://www.marksdailyapple.com/lectins/#axzz2qKZy6KHQ
2. Cordain L, Toohey L, Smith MJ, Hickey MS. Modulation of immune function by dietary lectins in rheumatoid arthritis. The British journal of nutrition. 2000;83(3):207-17.
3. Pusztai A, Bardocz S. Biological effects of plant lectins on the gastrointestinal tract: metabolic consequences and applications. Trends in glycoscience and glycotechnology. 1996;8:149-66.
4. Liener IE. Nutritional significance of lectins in the diet. In: Liener IE, Sharon, N., Goldstein, I.J., editor. The lectins: properties, functions, and applications in biology and medicine. Orlando, Florida: Academic Press; 1986.
5. Vasconcelos IM, Oliveira JTA. Antinutritional properties of plant lectins. Toxicon. 2004;44(4):385-403.
6. Pusztai A, Ewen S, Grant G, Brown D, Stewart J, Peumans W, et al. Antinutritive effects of wheat-germ agglutinin and other N-acetylglucosamine-specific lectins. British Journal of Nutrition. 1993;70(01):313-21.
7. Lam SK, Ng TB. Lectins: production and practical applications. Applied microbiology and biotechnology. 2011;89(1):45-55.
8. Mishkind M, Keegstra K, Palevitz BA. Distribution of wheat germ agglutinin in young wheat plants. Plant physiology. 1980;66(5):950-5.
9. de Moya CC, Grant G, Fruhbeck G, Urdaneta E, Garcia M, Marzo F, et al. Local (gut) and systemic metabolism of rats is altered by consumption of raw bean (Phaseolus vulgaris L. var. athropurpurea). British Journal of Nutrition. 2003;89(3):311-8.
10. Hamid R, Masood A. Dietary lectins as disease causing toxicants. Pakistan Journal of Nutrition. 2009;8(3):293-303.
11. Pusztai A. Dietary lectins are metabolic signals for the gut and modulate immune and hormone functions. European journal of clinical nutrition. 1993;47(10):691-9.
12. Kilpatrick D. Immunological aspects of the potential role of dietary carbohydrates and lectins in human health. Eur J Nutr. 1999;38(3):107-17.
13. Banwell J, Howard R, Kabir I, Costerton J. Bacterial overgrowth by indigenous microflora in the phytohemagglutinin-fed rat. Canadian journal of microbiology. 1988;34(8):1009-13.
14. Miyake K, Tanaka T, McNeil PL. Lectin-Based Food Poisoning: A New Mechanism of Protein Toxicity. PloS one. 2007;2(8):e687.
15. Rodhouse J, Haugh C, Roberts D, Gilbert R. Red kidney bean poisoning in the UK: an analysis of 50 suspected incidents between 1976 and 1989. Epidemiology and infection London, New York NY. 1990;105(3):485-91.
16. van Buul VB, F.J.P.H. Health effects of wheat lectins: a review. Journal of Cereal Science. 2014.
17. De Mejía EG, Prisecaru VI. Lectins as bioactive plant proteins: a potential in cancer treatment. Critical reviews in food science and nutrition. 2005;45(6):425-45.
18. Marinangeli CP, Jones PJ. Pulse grain consumption and obesity: effects on energy expenditure, substrate oxidation, body composition, fat deposition and satiety. British Journal of Nutrition. 2012;108(1):46-51.
19. Council GLN. What’s to Gain from Grains? An update of the scientific evidence 2013.
20. Council GLN. Lifting the Lid on Legumes. A guide to the benefits of legumes. 2013.
21. Jayalath VH, de Souza RJ, Sievenpiper JL, Ha V, Chiavaroli L, Mirrahimi A, et al. Effect of Dietary Pulses on Blood Pressure: A Systematic Review and Meta-analysis of Controlled Feeding Trials. American Journal of Hypertension. 2014;27(1):56-64.
22. Bazzano LA, Thompson AM, Tees MT, Nguyen CH, Winham DM. Non-soy legume consumption lowers cholesterol levels: A meta-analysis of randomized controlled trials. Nutrition, metabolism, and cardiovascular diseases : NMCD. 2011;21(2):94-103.
23. Sievenpiper JL, Kendall CW, Esfahani A, Wong JM, Carleton AJ, Jiang HY, et al. Effect of non-oil-seed pulses on glycaemic control: a systematic review and meta-analysis of randomised controlled experimental trials in people with and without diabetes. Diabetologia. 2009;52(8):1479-95.

Lentils reverse damaging effects of high blood pressure

Large population studies indicate that people who eat beans and soy foods at least four times a week are less likely to develop heart disease.¹ It was thought that legumes had this effect due to their ability to reduce LDL cholesterol.² However, a recent study in animals has brought a new idea to light.

A meta analysis of intervention studies on humans published this month indicates eating legumes significantly lowers blood pressure in people with high blood pressure as well as in people with normal blood pressure.³ The analysis of eight different trials found that when an average of one cup of legumes, including faba beans, lentils, chickpeas and beans, was substituted for foods of the same energy value there was a 2.25 mmHg reduction in blood pressure. A reduction of 2 mmHg is clinically relevant for lifestyle modification given that similar reductions are achieved with a low salt diet (4-5mmHg).⁴

A Canadian study in animals has found a new clue that may explain just how legumes are having this effect on blood pressure. The study, conducted in rats, showed that adding lentils to the diet can effectively block the increase in blood pressure that occurs with age. The findings also indicate that eating lentils can reverse the changes that occur in blood vessels as a result of high blood pressure.⁵

According to lead investigator Dr. Peter Zahradka, "These are amazing results, since they provide a non-pharmacological way of treating diseases associated with blood vessel dysfunction."

The investigation was undertaken after results from a clinical trial in 2013 indicated eating ½ cup a day of legumes, specifically a mixture of beans, peas, lentils and chickpeas, can improve blood flow to the legs of persons with peripheral artery disease, a condition that is closely linked to heart disease and diseases of the blood vessels.⁶

"The most notable finding of the latest study was the fact that lentils could alter the physical properties of blood vessels so that they resembled the vessels found in healthy animals," says

Dr. Zahradka. While human studies will still be needed to confirm these findings it does provide an interesting insight into how legumes may help prevent heart disease.

The Grains & Legumes Nutrition Council (GLNC) has commissioned the University of Wollongong to analyse data from a large Australian-based study to find out if there is a link between eating legumes and risk of heart disease in an Australian population. Results are expected later this year.

GLNC recommends Australians enjoy legumes such as lentils at least 2 - 3 times every week. Both dried and canned legumes are great additions to many meals. To reduce the salt in canned legumes, drain the canning liquid and rinse the legumes well.

For meal and snack ideas using legumes visit www.glnc.org.au

References:

1. Bazzano LA et al. Legume Consumption and Risk of Coronary Heart Disease in US Men and Women. Arch Internal Medicine. 2001;161(21):2573-8
2.  Bazzano LA et al. Non-soy legume consumption lowers cholesterol levels: A meta-analysis of randomized controlled trials. Nutrition, Metabolism and Cardiovascular Diseases. 2011;21(2):94-103
3. Jayalath VH, et al. Effect of Dietary Pulses on Blood Pressure: A Systematic Review and Meta-analysis of Controlled Feeding Trial. American Journal of Hypertension. 2014;27(1):56-64
4. Heart Foundation of Australia. Guide to management of hypertension, 2009.
5. Hanson MG, Zahradka P, Taylor CG. Lentil-based diets attenuate hypertension and large-artery remodelling in spontaneously hypertensive rats. British Journal of Nutrition. DOI: http://dx.doi.org/10.1017/S0007114513002997
6. Zahradka P et al. Daily non-soy legume consumption reverses vascular impairment due to peripheral artery disease. Atherosclerosis. 2013;230(2): 310–314

Global wheat bashing prompts an independent review

 

Claims that wheat is making people fat and sick have been propelled into the public’s view in recent years via books such as Wheat Belly and Grain Brain as well as wheat deprived diet plans such as Paleolithic diets and the gluten free phenomenon. In response to this increasing anti-wheat sentiment, independent researchers from the UK and the Netherlands have teamed up to review the accusations which underpin the claims that wheat has adverse health effects.

 

In this recent review, to obtain ensure the quality of the research the authors used set guidelines to search the scientific literature and critically evaluated the controlled scientific articles they included in this review. Based on their review the authors have discredited claims that wheat is harmful to health and causes weight gain. Their overriding conclusion was the claims which underpin the argument for the general population to eliminate wheat are not substantiated by scientific evidence.

 

In contrast to the unsubstantiated claims wheat is harmful to health, the authors highlight the body of evidence from scientific studies linking whole grain and high fibre wheat consumption with significant reductions in risks for type 2 diabetes, heart disease, and improved long term weight management.(1)

 

The following conclusions from the review address the key arguments supporting anti-wheat claims.

 

1. “Increasing wheat consumption parallels the increase in waist size”

• While it is true wheat consumption parallels increase in waist size, it is not valid to consider them as the cause of each other as this statement implies. For example increases in wheat consumption also parallels sales of cars, mobile phones and sports shoes – but to imply that they cause each other is ridiculous.
• In addition, the increases in wheat consumption has a much longer history than the more recent drastic increases of obesity, which has also occurred in populations that eat little wheat, such as several Asian countries. For centuries, there have been populations who consume wheat-based breads and other wheat products as the main source of their energy intake, such as in Turkey, without increases in weight gain of the population.

 

2. “Wheat free diets induce weight loss”

• The limited availability of wheat-free foods may itself lead to a reduced overall intake of food and energy. Weight loss is not induced by the absence of wheat but rather a decrease in total energy intake, a dieting-related phenomenon which occurs during virtually all energy restricted diets.

 

3. “Wheat opioids are so addictive that they cause people to be unable to control their eating, and removal of wheat from the diet causes withdrawal”

• The gluten proteins of wheat and other grains can be divided into two fractions, the gliadins and the glutenins. Incomplete digestion of gliadin has been shown to release a peptide, called gliadorphin which when injected into laboratory tests in rats was shown to induce opiate like effects. However, gliadorphin cannot be absorbed by the intestine and therefore cannot enter the blood stream nor have an effect on the cells of the central nervous system.
• There are no studies in which gliadorphin has been shown to be absorbed in intact form by the intestine and no evidence that gliadin either stimulates appetite or induces addiction like withdrawal effects.  

 

4. Whole-wheat bread has a Glycaemic Index (GI) of 72, which is higher than that of sugar (GI = 59)

• In the first instance the GI Values which support this claim are inaccurate with the internationally accepted average GI of sucrose being 67, white wheat bread being 70 and wholemeal wheat bread being 65.9.
• This statement implies that, based on GI, consuming sugar is better for your health than eating wheat which is a misinterpretation of the use of GI. The GI of carbohydrate food is one measure of carbohydrate quality and should be taken into account with other feature including nutrient density, fibre content, phytonutrient content and whole grain content.

 

The Australian Context

 

As wheat is the most consumed grain food in Australia, it makes a significant contribution to the Australian diet. Grain foods contribute a range of essential nutrients to the Australian diet including fibre, folate, niacin, thiamine, iron, zinc, magnesium, protein and carbohydrates. (2)

 

Australian and international dietary guidelines recommend people eat grain foods (including wheat foods), choosing mostly whole grain and high fibre options.(3) Unlike recommendation to eliminate wheat these dietary recommendations are substantiated to provide adequate nutrition, reduce risk of disease and promote a healthy weight.

 

What about people with coeliac disease, wheat allergy, gluten intolerance?

 

While dietary guidelines recommend a variety of grain foods within a balanced diet, it is important to note that there are individuals who cannot tolerate wheat or gluten in their diet. For people with diagnosed coeliac disease, wheat allergy or gluten sensitivity the avoidance of wheat is essential in order to treat or manage these conditions.

 

It is equally important to note that these conditions affect a small percentage of the population.

 

Where coeliac disease, a food allergy or sensitivity is suspected the Grains & Legumes Nutrition Council (GLNC) encourages individuals to seek a qualified medical practitioner to obtain a medical diagnosis. In the case of coeliac disease, a food allergy or sensitivity GLNC recommends individuals seek guidance from an Accredited Practising Dietitian to provide individualised dietary advice to ensure a balanced diet.

 

A final word...

 

Despite the lack of scientific evidence, it is likely the claims wheat is harming the health of the general population are likely to continue to make headlines, confuse consumers and influence food choices around the world in 2014. This was highlighted in a recent survey from the US in which over 500 dietitians identified an anti-wheat sentiment as the top nutrition and food trend in 2014.(4)

 

With demand for nutrition information at an all-time high, Australians need evidenced based advice and guidance now, more than ever, to cut through the clutter. It is good to see robust reviews such as this review and Julie Jones’ review on this topic (5) breaking through the noise to provide evidence-based information rather than anecdotal musings.

 

 

References:

1. Brouns FJPH, van Buul VJ, Shewry PR. Does wheat make us fat and sick? Journal of Cereal Science. 2013;58(2):209-15.
2. McLennan WP, A. . National Nutrition Survey. Nutrient intakes and physical measurements. Australia 1995. . ABS Cat No 48050 Canberra: Australian Bureau of Statistics. 1998.
3. NHMRC. Australian Dietary Guidelines. 2013. Accessed online January 2014.
4. 14 Top Diet Trends For 2014 2013 [cited 2014 January ]. Available from: http://www.prnewswire.com/news-releases/14-top-diet-trends-for-2014-237303161.html.
5. Jones J. Wheat belly-an analysis of selected statements and basic theses from the book. Cereal Foods World. 2012;57(4):177-189(4):177-89.

Legumes linked to better diet quality

Australian cohort links between legume consumption and overall diet quality

Article written by Joanna Russell, Associate Lecturer in the Faculty of Social Sciences at the University of Wollongong.  Her research interests focus on assessing diet and health outcomes in large cohorts.

The range of benefits from eating legumes regularly includes a good, inexpensive dietary source of plant protein and dietary fibre. In addition, they are a low glycaemic index food and also provide small amounts of iron, zinc, magnesium and calcium(1). Evidence to date suggests that legumes may play a role in reducing the risk of cardiovascular disease in adults due to their ability to improve serum total cholesterol and LDL cholesterol concentrations, but additionally they could have other health benefits(2, 3). 

Legumes are one of the main food types which make up the Mediterranean type diet, a diet that is high in fruit, vegetables, legumes and fish as well as olive oil being the main source of fat. The research has constantly reported the benefits of consuming this type of diet such as reducing the risk of mortality as well as reducing the risk of developing diabetes and obesity(4). Indeed, high legume consumption was found to be consistent with higher diet quality when adhering to the Mediterranean Diet. Tortosa et al (5) investigated the incidence of Metabolic Syndrome in a cohort of university graduates and reported the incidence of Metabolic Syndrome increased with decreasing adherence to the Mediterranean Diet.

However, the Mediterranean type diet is not commonly consumed outside of this European region although Greek migrants are reported to retain this type of diet after settling in Australia(6). In other countries such as Australia, suggested diets beneficial to health are provided through published dietary guidelines(7). These recommendations include regular consumption of legumes as part of a healthy diet either as a vegetable or as a meat alternative. Although the most recently published Australian Dietary Guidelines(8) do not provide specific recommendations for the amount of legumes to consume a week, the Grains and Legumes Nutrition Council suggest eating legumes 2-3 times a week as part of a healthy diet.

With the new dietary guidelines in mind, the quantified recommendations from the Grains & Legumes Nutrition Council legume consumption has been explored in a cohort of older adults and their overall diet quality in terms of adhering to the published Australian dietary guidelines. Preliminary findings will be presented at the Nutrition Society of Australia’s Annual Scientific Meeting in early December that suggest, similar to previous evidence, adults aged 49 years and over are not eating adequate amounts of legumes as recommended by the published guidelines. However, individuals who did consume at least two serves per week also had higher diet quality scores(9). These findings require further investigation, particularly as we have previously found in this cohort that individuals with higher total diet scores had a reduced risk of mortality, a reduced risk of impaired fasting glucose as well as better quality of life and functional ability (10-12). 

Future research is necessary to determine whether legumes, although a small component of the overall diet, play a role in the health benefits derived from eating a healthy diet as recommended by published dietary guidelines.

References

1. Bazzano La HJOLG, et al. Legume consumption and risk of coronary heart disease in us men and women: Nhanes i epidemiologic follow-up study. Archives of Internal Medicine. 2001;161(21):2573-8.
2. Jukanti AK, Gaur PM, Gowda CLL, Chibbar RN. Nutritional quality and health benefits of chickpea (Cicer arietinum L.): a review. British Journal of Nutrition. 2012 Aug;108:S11-S26.
3. Bazzano LA, Thompson AM, Tees MT, Nguyen CH, Winham DM. Non-soy legume consumption lowers cholesterol levels: A meta-analysis of randomized controlled trials. Nutrition, Metabolism and Cardiovascular Diseases. 2011;21(2):94-103.
4. Schröder H. Protective mechanisms of the Mediterranean diet in obesity and type 2 diabetes. Journal of Nutritional Biochemistry. 2007;18(3):149-60.
5. Tortosa A, Bes-Rastrollo M, Sanchez-Villegas A, Basterra-Gortari FJ, Nũnez-Cordoba JM, Martinez-Gonzalez MA. Mediterranean diet inversely associated with the incidence of metabolic syndrome: The SUN prospective cohort. Diabetes Care. 2007;30(11):2957-9.
6. Kouris-Blazos A, Gnardellis C, Wahlqvist M, L., Trichopoulos D, Lukito W, Trichopoulos A. Are the advantages of the Mediterranean diet transferable to other populations? A cohort study in Melbourne, Australia. British Journal of Nutrition. 1999;82:57-61.
7. National Health and Medical Research Council. Dietary Guidelines for Australian Adults. Canberra: National Health & Medical Research Council; 2003.
8. National Health and Medical Research Council. Australian Dietary Guidelines. Ageing DoHa, editor. Canberra: Department of Health and Ageing; 2013.
9. Russell J, Flood V, Broome M, editors. Do older Australians eat enough legumes? Nutrition Society of Australia's Annual Scientific Meeting; 2013 3-6 December 2013; Brisbane, Queensland.
10. Russell J, Flood V, Rochtchina E, Gopinath B, Allman-Farinelli M, Bauman A, et al. Adherence to dietary guidelines and 15-year risk of all-cause mortality. British Journal of Nutrition. 2013;109:547-55.
11. Gopinath B, Rochtchina E, Flood VM, Mitchell P. Diet quality is prospectively associated with incident impaired fasting glucose in older adults. Diabetic Medicine. 2013;30(5):557-62.
12. Gopinath B, Russell J, Flood VM, Burlutsky G, Mitchell P. Adherence to Dietary Guidelines Positively Affects Quality of Life and Functional Status of Older Adults. Journal of the Academy of Nutrition and Dietetics. 2013:http://dx.doi.org/10.1016/j.jand.2013.09.001.