Now a man is claiming he's busting the biggest diet myths, to expose an industry growing fat with our desire to lose weight.

So are we being sold a pack of big, fat lies?

Lawyer and author David Gillespie says this country's massive weight loss industry is based on nothing but lies.

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“Most diets work for a little while. All diets don't work when you measure it over two years or more,” he said.

They're extraordinary claims from a lawyer with no medical background, or qualifications in nutrition. However, what Gillespie lacks in medical knowledge, he makes up in experience.

He shed forty kilos without exercise, studied hundreds of diets, and ignored them all.

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“All I did was stop eating sugar - that is all I did. I didn't change anything else about my life,” he said.

Professor David Colquhoun is a cardiologist with 30 years’ experience investigating diets and their impact on his patients’ health, and he is critical of Gillespie's research.

“You've got to cut back on calories, and exercising is actually an important part of health per say. Even if you don't lose weight, going for a walk an hour most days halves your risk associated with obesity. That is data from 88,000 nurses, followed for 25 years - solid data,” Professor Colquhoun said.

Diet myths rebuked

The Australian weight loss industry recorded profits in the vicinity of $63 million last year.

Gillespie's latest book - 'Big Fat Lies: How the diet industry is making you sick, fat and poor' - picks apart some of the world’s most popular weight loss methods.

“I've then gone through the research on that type of diet to say what the research says; will the diet work; how long will it work; and what are the results that come back to years later,” Gillespie explained.

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He says basically diets don't work, and that's what’s turned us into a nation of diet junkies.

“People can't stay on them for any significant period of time, and just like any other kind of calorie-restricting diet, when you take the measurement out to two years, people are in general weighing at least as much, if not more,” he added.

Gillespie’s advice is to avoid fructose sugar laden products, as well as processed foods.

“I shop the outside of a supermarket. I shop the things someone probably would have bought if they'd been shopping in 1830,” he said.

Gillespie says to shop where you'll find primarily whole foods – fruits, vegetables, meats and breads. He says despite what we've been told, seed oils aren't good for us and that our body is built to deal with animal fats, not vegetable oils.

But it's probably the author's claims that exercise has no impact on weight loss that has medical practitioners up in arms.

“I'm saying if the reason you want to exercise is to lose weight, then you'll lose more weight, or have the same effect, by sitting still,” Gillespie concluded.

• Big Fat Lies by David Gillespie - www.penguin.com.au
• How Much Sugar? - www.howmuchsugar.com