Eat less, exercise more. Weight loss is a simple equation, or is it? Recently at the Australian Institute of Food Science and Technology conference I was intrigued to hear a number of speakers mention how the type of bacteria living in our digestive system can influence our weight.

Does that mean if I eat a whole lot of probiotic yogurt I will magically lose that extra padding around my stomach? It’s not quite that simple.

Our digestive system is teeming with microorganisms. In fact our body contains more bacteria than cells. We have around 10 trillion cells but around 100 trillion bacteria. In recent years scientists have discovered just how essential they are for health including:

• stimulating the immune system
• breaking down toxins and carcinogens in food
• fighting against bad bacteria such as e.coli, salmonella and clostridia
• fermenting food to release and absorb nutrients
• regulating inflammation
• regulating energy uptake from the gut

There are many different types of bacteria in our digestive system and, just like people in the world, some are more helpful than others. It’s all about having the right balance. On the beneficial bacteria side we have names such as bifidobacteria, lactobacilli (found in probiotic yogurt) and bacteriodes. On the other side we have e.coli and firmacutes, amongst others.

Lean people tend to have a better balance with more of the good bacteriodes while obese people have more firmicutes. For weight loss, there is nothing cute about firmicutes: these bacteria pull more calories out of food as it passes through the digestive system and store it as fat for later use.

So we want more bacteriodetes and less firmacutes. How do we do it?

When mice are fed a high fat diet, their gut flora changes to less bifidobacteria and bacteriodes, and more firmacutes, and they pack on the fat. When they are fed beneficial bacteria strains, in one study lactobacillus rhamnosus and in another P. vulgaris, they lose fat even though there is no change in energy intake. I love that idea! The bacteria actually change the way that energy and fat are metabolised.

Okay, eat less fat and more probiotic yogurt. But the story still isn’t that simple. These studies were done on mice, not humans. Until we have results from human clinical trials we can only assume the same effect will happen in humans.

In addition, a recent study from Iran suggests that lactobacillus in probiotic yogurt might actually increase body weight while polyphenol rich foods such as apples, pears, grapefruit and green tea promote weight loss partly because they suppress firmacutes action. I still think probiotic yogurt is a great food so what am I going to eat this week in an attempt to optimise the beneficial bacteria in my digestive system and hopefully my chances of weight loss?

• Swiss Muesli for breakfast, including probiotic yogurt, polyphenol rich apples and oats which act as a prebiotic (like fertiliser for the beneficial bacteria).
• Green tea instead of black to sip on while I write.
• Pears for a polyphenol rich, high fibre snack when I get hungry.

A final note. Weight loss is still about less energy in and more energy out. Just because a food is healthy doesn’t mean we can pig out on it!