How you felt about Dr. Mehmet Oz's Senate grilling the other day probably depends on how you feel about cooked goose. Or perhaps you're off cooked goose. Possibly it's one of those verboten diet foods; maybe it gives you goose caboose. I've lost track.

Dr. Oz, handsome star of the television screen and operating theatre, appeared before a U.S. Senate committee on consumer protection to talk about his questionable endorsements of various enchanted potions that would cause fat to melt away like butter on hot popcorn. Take green coffee bean extract, for example, which he had promoted on his popular Dr. Oz show this way: "You may think magic is make believe, but this little bean has scientists saying they've found the magic weight-loss cure for every body type." (I'm not sure how often you're allowed to say "magic" in medical school before they kick you out.)

This was not Dr. Oz's first time at the magic-bean rodeo. He had also raved about the slimming properties of garcinia extract and raspberry ketones, which frankly sound more like the ingredients of a hippie pot luck than the path to long-term weight loss.

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Senator Claire McCaskill, clearly the star of Top Chef Capitol Hill, relished her job as she turned Dr. Oz over the coals: "I don't get why you say this stuff, because you know it's not true," she said. "So why, when you have this amazing megaphone, and this amazing ability to communicate, why would you cheapen your show by saying things like that?"

In his defence, Dr. Oz suggested, essentially, that his viewers were too stupid to understand that you should never trade magic beans for a cow on the way to the fair: "We have to simplify complicated information," he said. "We have to make the material seem interesting and focus on the 'wow' factor."

It was great theatre, but I had the niggling feeling that it was just that: an amusing sideshow to distract from the larger backdrop, which is that a lot of people make a lot of money by keeping a lot of people fat. The diet industry – slimming companies, supplement peddlers, bestselling authors – grows apace with the Western world's expanding waistlines. You don't need to be Newton to do the math, but if you were P.T. Barnum you might appreciate the success of a business that thrives on its own failure.

Take the fact that, in the U.S., the diet-supplement industry – the people who promise to melt pounds fast! In days! Without leaving the couch! – is worth upwards of $14-billion, according to The Wall Street Journal. Even better, a vaguely regulated industry generates whopping profits of almost 12 per cent, when averaged out. There is gold in our wobbly hills.

The new documentary Fed Up provides an illuminating glimpse into the fat-industrial complex (well, more the sugar-industrial complex, but it all ends up in the same place). Rather than blaming obesity on lack of willpower or couch-spuddery, filmmakers Katie Couric, Laurie David and Stephanie Soechtig follow the money trail to the real source of the problem: Hugely powerful food corporations that hold the whip hand with politicians and their lobbyist minions.

Consider what happened when Fed Up was released in theatres: The Grocery Manufacturers Association, terrified that the curtain was being pulled back, set up a propaganda website called Fed Up Facts, camouflaged to look like it was the film's official home. The best advice Woodward and Bernstein ever received holds true today: "Follow the money."

There is a remarkable sleight of hand going on. Coca-Cola wants to be part of the "obesity solution," and suggests you pedal a bike for 23 minutes and reward yourself with a Coke. The authors of Grain Brain and Wheat Belly want you to buy their books and try their diets when all evidence suggests that you are more likely to marry Leonardo DiCaprio than keep weight off permanently by following a trendy regime. And Dr. Oz maintains that he makes no money when he extols the latest fat-melting potion, but it helps pull more viewers to his show, and readers to his books.

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It was ever thus. One of my favourite books of the past few years is Louise Foxcroft's Calories and Corsets, a centuries-spanning global history of the diet industry and its ingenious methods of entrapment. Let us not forget 19th-century snake oil success Slenda Fat Reducing Chewing Gum, or the bestseller I Prayed Myself Slim, or the immortal slogan for RyKrisp crackers, "Nobody Loves a Fat Girl."

"The diet industry is all about exploitation and profit," Ms. Foxcroft writes, having examined failed weight-loss miracles from acai berries to desiccated thyroid (yum!) "Many foul and extraordinary ways to get thin have been advertised and tried …. And a lot of them were, are, just scams and tricks conjured up by doctors, charlatans and gurus." It's not just one guru, or one charlatan, and as time goes by two things keep getting bigger: our pants, and their wallets.