There has been an explosion of probiotic products on the market recently, primarily in the form of yogurts and supplements, and companies have done an excellent job of convincing us that these products are essential for optimal health. But what are the real benefits of probiotic consumption, if any? Based on commercials, the main benefit of probiotics seems to be the power of belly dancing!
While boosting your healthy gut microflora is unlikely is improve your rhythm, probiotics do have a very real impact on our health. What are the true effects of probiotics on the body and health? And how can you get the maximum benefits? These questions are too complicated to be answered in a single post, so we will focus on the role of probiotics on body weight today (and hopefully tackling other aspects of probiotics and health at a later date!).
Before we can look at the effects of probiotics on health we need to take a step back and review gastrointestinal physiology. The human gastrointestinal tract contains about 1014 bacteria, most of which live in the colon or large intestine. There are thousands of different bacterial types and everyone has a slightly different profile (1). This is significant as certain bacteria promote disease, whilst others promote health. The list of diseases that are either prevented or promoted by the gut bacteria is extensive and ranges from colorectal cancer to autoimmune and allergic diseases (2).
Evidence that gut bacteria can influence body weight, in humans, first came in 2006 (earlier animal studies found similar results). A group of researchers noticed that obesity was associated with an imbalance in the proportion of two groups of bacteria – people with a higher body weight tended to have a reduction in Bacteroidetes group and an increase in the Firmicutes group (3). They went further and found that by transplanting “obese mouse microflora” into a mouse who lacked gut bacteria, the mouse became obese. Conversely, the opposite is also true. If they transplanted bacteria from a lean mouse into a mouse without any bacteria, it became lean (4). Ley et al. (3) also found that weight loss increases the proportion of Bacteroidetes relative to the Firmicutes. Since then several other studies have been conducted to try to determine which types of bacteria promote weight gain and which help maintain a lean body weight. Unfortunately, the waters are muddy as there are literally thousands of different strains to explore.
Furthermore, a few key questions remain:
1) How do the bacteria affect body weight?
2) Can an individual’s bacteria profile be changed to promote weight loss? And if so how?
How do the bacteria affect body weight? There are a few theories with some evidence to support them. The first theory is that the gut bacteria affect body weight by increasing the efficiency by which energy (calories) can be extracted from food (4). Another suggestion is that the gut bacteria could reduce fat oxidation, meaning that a particular bacterial profile would inhibit a person’s ability to burn fat and thus increase body weight (5). Still another suggestion is that the byproducts produced when bacteria breakdown food have the ability to regulate an individual’s appetite and/or their immune system (6). At present it seems like many, if not all, of these different mechanisms are at work.
Can we manipulate the gut bacteria to promote weight loss and if so how do we do that? Bacterial colonization begins at, or possibly before, birth and can be influenced throughout the lifespan by a variety of factors, of which diet is a key contributor. This means that eating a probiotic yogurt can change the bacteria in your gut. Unfortunately, so can drinking unclean water – traveller’s diarrhea anyone? Most of the research so far suggests that you need to maintain intakes of the healthy bacteria to sustain changes to your gut bacteria.
Another way to manipulate the gut bacteria is to eat prebiotics. Prebiotics are a type of dietary fibre that the good-for-you gut bacteria love to eat – when prebiotics are eaten, your gut bacteria colonies grow and thrive. Fructo-oligosaccharides (FOS) found in sunchokes, garlic, onions and leeks are just one class of prebiotics. For more information on prebiotics, click here.
This is all very promising as it seems we can effectively alter an individual’s gut bacteria. The problem? It’s still unclear which ones, if any, will promote weight loss. The ones typically found in yogurt, bifidobacteria and lactobacillus, have been found to have many health benefits but their role in controlling body weight is still unclear. For an excellent review of the current state of knowledge, see Delzenne et al. 2011. Some studies find yes, some no – again the discrepancy is likely due to the different effects of the different strains. To add to the confusion there are so many different factors that affect weight gain. Research in humans is messy and it is hard to determine what changes are due to the probiotics and what changes are due to other diet and lifestyle confounders.
No Baloney’s advice? There is too little evidence to recommend a probiotic that will promote weight loss. However, research suggests that the lactobacillus and bifidobacteria strains found in yogurts help maintain a healthy gastrointestinal tract. Probiotic yogurts have increased numbers but any yogurt will have some healthy bacteria. As always, watch the sugar content and calories in these yogurts, especially if weight loss is a goal! Aim for < 14 g sugar per serving.
Stay away from those artificial sweeteners too, as they are also linked to increased body weight. Try plain lower-fat yogurt (2 – 4% milk fat) and add your own fruit, honey, bran buds, etc. for flavour and texture. For an extra protein boost, we suggest Greek-style yogurt, which contains up to triple the protein content of conventional yogurt.
(1) Wallace TC, Guarner F, Madsen K, Cabana MD, Gibson G, Hentges E, et al. Human gut microbiota and its relationship to health and disease. Nutr Rev 2011; 69(7):392-403.
(2) Prakash S, Rodes L, Coussa-Charley M, Tomaro-Duchesneau C. Gut microbiota: next frontier in understanding human health and development of biotherapeutics. Biologics 2011; 5:71-86.
(3) Ley RE, Turnbaugh PJ, Klein S, Gordon JI. Human gut microbes associated with obesity. Nature 2006; 444(7122):1022-1023.
(4) Turnbaugh PJ, Ley RE, Mahowald MA, Magrini V, Mardis ER, Gordon JI. An obesity-associated gut microbiome with increased capacity for energy harvest. Nature 2006; 444(7122):1027-31.
(5) Backhed F, Manchester JK, Semenkovich CF, Gordon JI. Mechanisms underlying the resistance to diet-induced obesity in germ-free mice. Proc Natl Acad Sci USA 2007; 104(3):979-984.
(6) Deshpande G, Rao S, Patole S. Progress in the field of probiotics: year 2011. Curr Opin Gastroenterol 2011; 27(1):13-18.