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As a healthcare practitioner, you may already be aware that obesity levels have been rising exponentially for many years, causing both physical and emotional problems for those affected, whilst also placing a substantial burden on the National Health Service. Diet ‘fads’ seemingly come and go, with every new diet book promising life-changing and sustainable results. But the truth is, that many of these diets fall short of their claims, leading many to wonder what they are doing wrong.
Could it be then that there is a missing link, and we have all been looking in the wrong places? Is it possible that the gut microflora may hold some answers to this elusive weight loss issue?
Evidence has already shown that probiotic bacteria have many beneficial physiological effects, including nutrient assimilation and energy regulation, and this has prompted scientists to begin research into a possible link between gut microbiota (visit the Probiotics Learning Lab for more) and weight loss (or gain). In this post we will be looking at whether taking a simple probiotic supplement could aid in weight loss.
There have been a number of studies exploring the possibility of using probiotics and/or prebiotics for weight loss. Although current evidence is inconclusive in terms of suggesting a specific probiotic strain, the early research looks promising, and definitely encourages further studies to find out more.
Before we delve in to the clinical studies it is important to consider what the possible connection between the gut flora and weight management could be. It is already known from earlier studies performed on mice that certain species of bacteria in the gut can cause weight gain, and other species seem to promote weight loss. This was originally shown when researchers transplanted some of the gut microbes from over-weight mice in to thin mice, and some of the microbes from thin mice in to over-weight mice. This research1 proved that swapping the microbiota, and therefore changing the gut environment, caused the thin mice to put on weight, and the fat mice to lose it.
Controlling inflammation in the body is one theory that scientists are considering when looking at the role of the microbiome in weight loss. The diagram below shows that our gut flora, produces many different biologically active substances that may affect our weight. For example, gut bacteria produce bile acids, which affect how we break down and absorb fats from our diet. They also contribute to the production of short-chain-fatty-acids (SCFAs) that influence our energy levels, as well as how effectively our gut lining is able to heal. Reduced levels of SCFAs can lead to the development of ‘leaky gut’, which in turn increases systemic inflammation.
Inflammation in the body is a key factor in obesity, as the body holds on to fat in order to safely store circulating fat-soluble toxins. This is then a perpetuating cycle, as increased body fat then leads to even greater inflammation.
Scientists think that the effect of probiotics on our digestion and absorption of fats could also be a contributory factor in how probiotics aid weight loss. One trial2 showed that certain strains of probiotic may reduce the amount of fat absorbed from the diet, which has the effect of reducing our total caloric intake and therefore increasing weight loss.
In this study, healthy volunteers were given 100g of a fermented milk drink daily for 7 days.The trial group was divided in to two, with one half of the volunteers receiving the fermented milk drink without any added probiotic, and the other half receiving the fermented milk drink enriched with the probiotic Lactobacillus gasseri SBT2055 (LG2055).
Faecal samples were taken from the study participants both before the commencement of the trial, and at intervals throughout the trial. Results showed that following the probiotic supplementation faecal fat levels were significantly higher, meaning that more dietary fat was eliminated than in the control group.
As a healthcare practitioner, you might know that different strains of bacteria do different things. Within the context of weight loss, whilst some strains appear to reduce fat absorption in the intestines, others may affect weight in other ways. One other possible explanation that scientists are looking at, is whether probiotics influence how hungry or satiated we feel.
Several mouse models have shown that a particular probiotic combination can increase levels of GLP-1 in the intestine. GLP-1 is a satiety hormone that signals to us when we have eaten sufficient quantities of food. Higher levels of GLP-1 can therefore lead to people consuming smaller portions of food at each sitting, and therefore weight loss may result.
In one particular trial3, mice that had been given this specific probiotic combination (VSL#3) were shown to have an increased level of butyrate in their intestines. Butyrate is a short-chain-fatty-acid, that is known to stimulate the release of GLP-1.
As mentioned earlier, one of the many consequences of systemic inflammation is increased weight, or increased fat stored in adipocytes (fat cells). This in turn can lead to the possible development of insulin resistance, as fat accumulation in adipose cells interferes with insulin signalling and action. When cells become ‘resistant’ to insulin, more insulin needs to be produced in order to regulate the blood glucose levels. Insulin resistance puts pressure on the pancreas and indirectly on the adrenal glands also.
In 2017, researchers at Sao Paulo State University in Brazil, looked at the impact of probiotics on insulin resistance4. Using mice that had been fed a high fat diet (to induce changes in their gut flora), they found that by supplementing with Lactobacillus rhamnosus, L. acidophilus and Bifidobacterium bifidum they were able to reverse both the changes to the microflora, and also they were also able to reverse the obesity related insulin resistance that the mice had developed as a result of the high fat diet.
Presuming that humans respond similarly to these probiotics, as mice do, it would seem that taking a multi-strain probiotic formula that contains strains of Lactobacillus rhamnosus, L. acidophilus and Bifidobacterium bifidum might confer some protection against insulin resistance and inflammation, both of which have an impact on weight gain.
Other studies show that prebiotics such as FOS can increase levels of the satiety hormone, glucagon-like peptide (GLP-1), helping to reduce food intake and improving the blood lipid profile. For further information on prebiotics and weight loss, see the following article: The Uses of Prebiotics.
A meta-analysis recently published has concluded there is a lack of robust evidence that prebiotics or synbiotics aid weight loss5. Rather than a disappointing result, this is something that researchers in this field are already acutely aware of. It would seem that this meta-analysis study has been conducted prematurely, when we know the clinical trial research still has a long way to go. We shouldn't be disheartened by this publication but rather see it as a reminder of where we are in the research process. Watch this space!
Whilst a reduction in bloating is not precisely the same thing as a reduction in weight, losing inches from their stomach circumference is what most people really want, when they embark on a weight loss regime.
Clinical trials have been carried out on many different strains of probiotics to study their effect on abdominal bloating and distension.
One such double-blind, placebo controlled study6 in 2008, followed 41 female study participants, all of whom suffered with IBS-C (IBS with constipation) and complained of abdominal bloating and swelling at least twice per week. The participants were divided in to two groups and given either: a fermented dairy product containing Bifidobacterium lactis DN-173010 or placebo for 4 weeks.
The results showed that the probiotic group saw a significant reduction in both severity of bloating and duration/frequency of the symptom.
More research is still needed before we know the best strains of probiotic to take to achieve lasting weight loss, however there is a growing body of evidence to show that the microbiome does undoubtedly have an impact on our susceptibility/ability to either put on, or lose weight.
For further reading, you might be interested in the following: