Now the man behind it is determined to bust quite a few myths about what is really making us all so fat — and the results will surprise you.

While good food and exercise are no doubt crucial to a healthy body, leading diet and obesity expert Professor Tim Spector is turning conventional wisdom on its head.

Using cutting edge research, the Professor of Genetic Epidemiology at King’s College London, reveals the key role bacteria and microbes play in weight loss and how bad diet and the rise of antibiotics is killing them.

According to Professor Spector, who is author of The Diet Myth, many people view bacteria as the enemy without realising that some are actually crucial for a healthy gut and immune system.

In the documentary The Diet Myth which airs tonight on SBS, Prof Spector challenges everything we know about weight loss by looking at the link between diet, microbes and weight.

According to him, the link which was first explored a decade ago, gut bacteria isn’t only an indicator of obesity but can cause it.

Speaking to news.com.au, Prof Spector said modern society and diets were destroying our good gut bacterins, not helped by the increase in antibiotics, the rise in C-section births and our obsession with cleanliness.

To prove his point, the documentary features a Super Size Me type experiment starring his own son Tom, who eats only junk food for 10 days with astounding results.

Prof Spector said his son was a very happy guinea pig initially but he soon craved a salad.

“The idea was to recreate Super Size Me with the microbile on a slightly smaller scale realising that I also didn’t want to kill my son and he didn’t want to die,” he says in the documentary.

But would his microbes (bacteria) survive?

The results showed his gut microbes (or microbiome) had been destroyed and had lost 40 per cent or 1400 species in that short time.

“By day four I described it as almost being hung-over after every meal,” Tom said.

According to Prof Spector, these species of microbes and good bacteria are so essential as good bacteria is responsible for producing a lot of our vitamins and nutrients which in turn produce healthy chemicals.

“The more different species there are, the more different metabolites they produce, the more nutrients they can get out of the food the batter,” he said.

“The more healthy our immune system is the less obesity we have.”

Researchers also went to further extremes to test their theory that lack of diverse microbes are present in obese people with another researcher having stools from a man in an ancient African tribe inserted into his own body.

Prof Spector said the research showed why diet and exercise alone couldn’t explain why people gained weight.

Instead he said the rising use of antibiotics were affecting our guts, especially when consumed at a young age, could affect obesity levels later in life.

“Over the past 30 years people keep getting fatter so it’s obvious it (diet/exercise) isn’t working,” he said.

“Exercise is not enough to lose weight on its own. Only a small percentage of people can actually lose weight this way.”

His documentary and book also turn several myths on their head such as avoiding fatty food, saying no to carbs and subjecting ourselves to extreme diets.

All he insists any diet won’t work if our stomachs don’t have the keys (microbes) needed to regulate and break down our food properly in the first place.

He said babies born naturally had less chance of being obese because vital microbes were passed to the baby during delivery, which C-section babies don’t receive.

But it’s not all bad news, Prof Spector reckons there is hope for us yet.

Just eating probiotics which are found in yoghurts for example, root vegetables, nuts, olives and high-fibre foods can help counter the damage.

“Also let your children play in the dirt,” he said.

“The average Australian has 1/3 to 1/2 less microbes in their guts than people in African tribes and less diversity means less protection against allergies.

“By the time the average Australian is 18 they would have had 16-17 course of antibiotics in their lifetime. This seriously messes things up.

“It’s like waiting for an atomic bomb to go off.”

He said many farmers gave their animals antibiotics not to stave off or help with sickness but more because it made them fatter, a pattern he said was obvious in humans who had consumed antibiotics too.

“It’s a bad trend, we are working against evolution,” he said.

The Diet Myth premieres tonight at 8.30pm on SBS1.

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