For centuries yoghurt has been consumed because of its many healthful properties. Today yoghurt is purchased because of its taste and perceived health-giving attributes, specifically, the introduction of probiotics (positive bacteria) into our diet. In the marketing of many brands of yoghurt there are claims that the yoghurt contains "live cultures". This acknowledges the growing consumer awareness about health-giving foods. However, varying production methods mean big differences in the number of probiotics present.
Yoghurt is a product of the lactic acid fermentation of milk by the addition of a starter culture containing Streptococcus thermophilus and Lactobacillus delbrueckii ssp. bulgaricus. In some countries, however, less traditional microorganisms such as Lactobacillus helveticus and Lactobacillus delbrueckii ssp. lactis are mixed with the starter culture.
While the term "probiotic" is relatively new, the concept dates back to the beginning of the last century when Nobel Prize winner Ilya Ilyich Mechnikov associated the longevity of Bulgarian peasants with their intake of lactic acid bacteria derived from consuming large quantities of yoghurt. (In fact, the yoghurt starter culture Lactobacillus delbrueckii ssp. bulgaricus was named after Bulgaria.) In 1907, it was first suggested that ingested bacteria could have a positive influence on the normal microbial flora of the intestinal tract.
Probiotics are the beneficial bacteria that help our bodies maintain the right balance of "good" and "bad" bacteria in our digestive systems. We have some 140 trillion bacteria in our gut, over a kilo in weight, known as gut flora. They aid in the digestion of food, provide a constant supply of nutrients such as B vitamins and amino acids, produce important substances such as Vitamin K, improve mineral absorption and help the body fight off harmful bacteria. These good bacteria are essential for a healthy gut and crucial to our overall health and wellbeing.
Yoghurt is thought to be a better source of minerals and more readily absorbed than the minerals in raw milk. The process by which the yoghurt is made appears to dramatically alter the mineral distribution, making the minerals in yoghurt more bioavailable than those found in raw milk. In one study, yoghurt bacteria influenced the levels of certain B vitamins. During the trial, young women who consumed 100grams per day of probiotic yoghurt tested with increased levels of B vitamins - including Vitamin B1 (Thiamine), Vitamin B2 (Riboflavin) and Vitamin B6 (Pyridoxine) - in the blood plasma, demonstrating that the regular consumption of probiotic yoghurt foods is more beneficial than consuming milk alone(1).
Yoghurt appears well suited for individuals who are lactose intolerant. Lactose intolerance is due to insufficient amounts of the enzyme lactase; it results in difficulty digesting the disaccharide lactose, the main carbohydrate in milk and dairy products. In properly fermented yoghurt, however, the bacteria "digest" the lactose. This could mean that individuals suffering from lactose intolerance could consume yoghurt as part of their diet, which does seem to be true in many cases.
A number of studies have found that eating conventional yoghurt has positive effects on the lipid profile in the plasma of healthy women (2,3) and it did not matter if they were normal or high cholesterol participants. In particular the HDL (beneficial) cholesterol increased significantly during the trials.
Getting the balance right
The positive effects of probiotics and the importance of good gut bacteria for our digestive system and health have been largely ignored (4). Probiotics protect us in two ways. One is by competing successfully with potentially harmful microbes in our digestive tracts. This doesn't mean killing all of them but rather helping to establish a healthy probiotic population by out-competing the toxic microorganisms. Difficulties can occur when the probiotic bacteria in our intestines are unable to compete with an onslaught of harmful bacteria. More than 99 per cent of the intestines are bacteria from 500 to 1,000 different species, the rest are yeast or parasites. Some bacteria such as Escherichia coli (E. coli) can double their numbers in 20 minutes. The typical two-week course of high dose antibiotic treatment, as might be used for an ear infection, can wipe out most of the normal gut microbes in the short term. But poor quality (processed) foods, many food additives and synthetic chemicals can create an ongoing problem. As a result probiotics have been used to treat and prevent problems like diarrhoea (5), gut barrier dysfunction associated with inflammation and infection (6,7) and gastroenteritis (8).
The gut bacteria appear to have a direct effect on the overall health of our bodies. Having the right balance of bacteria in our guts is not only essential for good digestion but also for the prevention of chronic diseases.
A study in Western Australia found that probiotics and products containing probiotics may help young children with eczema (9). The children who took supplements of the probiotic Lactobacilli showed great improvements and the benefits lasted once the supplementation stopped(10,11). Similarly, recent studies suggest that babies whose mothers used probiotics during pregnancy and while breastfeeding were less likely to have eczema (12). The supplementation of probiotics for infants with eczema has also been hugely beneficial(13,14).
Other conditions that are improved with probiotic supplementation include:Cancer(15)Diabetes(16) Eating disorders(17)Gastric ulcers(18)Allergies(19)
Infection and sepsis (20,21)Inflammation (22) Nutrient synthesis and availability to the body(23) Multiple trauma (24) Immune function function (25,26) Vaccine response (27) Infant growth (28)
However, not all probiotics are the same and not all yoghurts have the same amount of probiotics. In fact our research showed huge differences in the level of probiotic bacteria in the yoghurts we tested. Eight brands of common yoghurt were tested to identify the number of probiotic bacteria in 100 grams of the product. The probiotic bacteria tested for included L. acidophilus, Bifidobacteria and L. casei (as per Chr. Hansen methodology).
The list below shows the number of live bacteria per 100 millilitres of yoghurt.Yoghurt Bacteria per 100mlSKI2,000,000UNCLE TOBYS120,000,000, ALNA300,000,000,YOPLAIT410,000000,
Unfortunately many of the yoghurts tested had low probiotic bacteria counts. In particular, the large commercial yoghurts had as little as 9,000 times fewer probiotic bacteria than the brand Mundella. This is largely due to the way the yoghurt is made. Both Vaalia and Mundella are "pot set," that is the bacteria are cultured in the containers in which they are sold. The highest count of 19 billion probiotic bacteria per 100 millilitre serve was in the Mundella organic range. These levels are in excess of most of the probiotc powders one can purchase from a chemist or health food store.
In the pot set method of making yoghurt, milk is put into individual containers along with the bacteria culture, the containers are sealed and then incubated. The incubation takes about eight hours and has to be at the perfect temperature to achieve the highest bacteria counts. The benefit of pot set yoghurt is that it creates the least disturbance to the bacteria. However, it is labour intensive and sensitive to disturbances. Pot set yoghurt is a much more precise science compared to making large vats of yoghurt. The small starting batch size of the pot set yoghurt allows for greater control and the ability to adjust conditions far greater than large vats of thousands of litres. This also means they can test and monitor sample types much more precisely. The quality of the starter culture of bacteria and the inoculation rates are also critical. There is much greater control over inoculation rates when it is done one pot at a time.
Other factors include freshness of the milk supply. Milk does not like being transported. It literally batters the fat molecules around. Large companies often source their milk from farms that are hundreds of kilometers away, while the smaller yogurt manufacturers often have milk hundreds of meters away and can access milk literally within hours of milking. Bacterial cell counts that naturally occur in milk and are eliminated via pasteurisation are directly proportional to time it takes to get to the processing plant and temperature. The closer the processing is to the milking the fewer cell counts.
By contrast, the larger brand yoghurts rely on a much more automated approach. The yoghurt is cultured with the milk in large vats then, under pressure, poured into the containers. Each additional step after the culturing of the bacteria creates a greater disturbance to the culture, thus lowering the numbers of each culture. In addition, culturing in large vats does not allow for the maximum number of bacteria cultures to be grown, resulting in extremely low bacterial counts.
So what does this mean for the health conscious consumer? Unfortunately the large commercial brands of yoghurt have little, if any, probiotic benefits.
I am often asked what the levels are like in yoghurt cultured at home. While I did not measure these levels they are likely to be a lot higher than the large commercial brands yet a lot lower than the pot set brands. Yoghurt making to achieve high levels of good bacteria is a real science.
Dr Peter Dingle is Associate Professor in Health and the Environment at Murdoch University, Western Australia and the author of "My Dog Eats Better Than Your Kids".
1,2 Fabian, E. and I. Elmadfa (2006). "Influence of Daily Consumption of Probiotic and Conventional Yoghurt on the Plasma Lipid Profile in Young Healthy Women." Annals of Nutrition and Metabolism 50(4): 1-8.
3 Kie_ling, G., J. Schneider, et al. (2002). "Long-term consumption of fermented dairy products over 6 months increases HDL cholesterol." European Journal of Clinical Nutrition 56: 843-849.
4 Isolauri.E et al, 2001, Probiotics-Effects on Immunity, American Journal of Clinical Nutrition, Volume 73, Issue 2, Pg 444.
5 Ahmed, M., Prasad, J., Gill, H., Stevenson, L., & Gopal, P., (2007). Impact of consumption of different levels of Bifidobacterium lactis HN019 on the intestinal microflora of elderly human subjects.The Journal of Nutrition, Health & Aging, 11, 26-31.
6 Kim, H.S., Park, H., Cho, I.Y., Paik, H.D. and E. "Dietary supplementation of probiotic Bacillus polyfermenticus, Bispan strain, modulates natural killer cell and T cell subset populations and immunoglobulin G levels in human subjects," J Med Food. 2006 Fall; 9(3):321-7.
7 Gill, H.S., Rutherfurd, K.J., Prasad, J., & Gopal, P.K. (2000). Enhancement of natural and acquired immunity by Lactobacillus rhamnosus (HN001), Lactobacillus acidophilus (HN017) and Bifidobacterium lactis (HN019). British Journal of Nutrition, 83, 167-176
8 Ee LC and Cohen MB (2000) Gastrointestinal infections in children. Curr Opin Gastroenterol. 2000 Jan;16(1):40-44
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10 Hauer, A. MMW Fortschr Med. 2006 Aug 31;148(35-36):34-6. Probiotics in allergic diseases of childhood. [Article in German.] Klin. Abt. fur Allgemeine Padiatrie Univ. -Klinik fur Kinder-und Jugendheilkunde, Graz.
11 Weston, S., Halbert, A., Richmond, P. and Prescott, SL. (2005) Effects of probiotics on atopic dermatitis: a randomised controlled trial. Archives of Disease in Childhood 2005;90:892-897
12 University of Maryland Medical Center (UMMC) (2006) Eczema (Available Online) www.umm.edu/altmed/ConsConditions/Eczema
13 Murch, SH. (2005) Probiotics as mainstream allergy therapy? Archives of Disease in Childhood 2005;90:881-882
14 Weston, S., Halbert, A., Richmond, P. and Prescott, SL. (2005) Effects of probiotics on atopic dermatitis: a randomised controlled trial. Archives of Disease in Childhood 2005;90:892-897
15 Lionettil E, Fico S, Maurogiovanni G, Cavallo L and Francavilla R. (2006) Treatment for Helicobacter pylori in children. Recent advances. Prog Med. 2006 Sep;97(9):472-6
16 Canadian Diabetes Association (CDA) (2006) Digestive Problems. (Available Online) www.diabetes.ca
17 Fuller, R. and Perdig-n, G. (2003) Gut Flora, Nutrition, Immunity and Health. Journal of Human Nutrition & Dietetics Volume 17 Page 159 - April 2004
18 Lionettil E, Fico S, Maurogiovanni G, Cavallo L and Francavilla R. (2006) Treatment for Helicobacter pylori in children. Recent advances. Prog Med. 2006 Sep;97(9):472-6
19 Hauer A (2006) Probiotics in allergic diseases of childhood. MMW Fortschr Med. 2006 Aug 31;148(35-36):34-6
20 Sanders ME. (2006) Summary of Probiotic Activities of Bifidobacterium lactis HN019. J Clin Gastroenterol. 2006 Oct;40(9):776-83
21 Douglas.L, Sanders.M, 2008, Probiotics and Prebiotics in Dietetics Practice, Journal of the American Dietetic Association, Volume 108, Issue 3,pg 510. (Accessed 10th April 2008) Proquest
22,23,24 Kotzampassi K, Giamarellos-Bourboulis EJ, Voudouris A, Kazamias P, Eleftheriadis E. (2006) Benefits of a Synbiotic Formula (Synbiotic 2000Forte(R) in Critically ill Trauma Patients: Early Results of a Randomized Controlled Trial. Benefits of a Synbiotic Formula (Synbiotic 2000Forte(R)) in Critically Ill Trauma Patients: Early Results of a Randomized Controlled Trial. World Journal of Surgery. Oct 2006.Vol.30, Iss. 10; pg. 1848
25 Kim, H.S., Park, H., Cho, I.Y., Paik, H.D. and E. "Dietary supplementation of probiotic Bacillus polyfermenticus, Bispan strain, modulates natural killer cell and T cell subset populations and immunoglobulin G levels in human subjects," J Med Food. 2006 Fall; 9(3):321-7.
26, 27 Taylor AL, Hale J, Wiltschut J, Lehmann H, Dunstan JA and Prescott SL. .2006. Effects of probiotic supplementation for the first 6 months of life on allergen- and vaccine-specific immune responses. Clin Exp Allergy. 2006 Oct;36(10):1227-35
28 Sanders ME. (2006) Summary of Probiotic Activities of Bifidobacterium lactis HN019. J Clin Gastroenterol. 2006 Oct;40(9):776-83
Dr Peter Dingle (PhD) has spent the past 30 years as a researcher, educator, author and advocate for a common sense approach to health and wellbeing. He has a PhD in the field of environmental toxicology and is not a medical doctor. He is Australia’s leading motivational health speaker and has 14 books in publication.