Last Night's TV: Who Knows Best: Fighting the Fat / Channel 4<br/>The Great British Bake-Off / BBC2

Slim pickings for the ladies who munch

Competition – or "challenge", as it is usually called – is now television's monosodium glutamate, a flavour enhancer that can be added to virtually any social issue or subject to give it narrative zip. So, where once you might have had a consumer guide to weight-loss methods or a presenter-led cooking series, you now get Who Knows Best: Fighting the Fat and The Great British Bake-Off, programmes made with completely different (and quite possibly incompatible) ingredients, but both carrying the same distinctive flavour of confected head-to-head.

Who Knows Best would be inconceivable without it, since Channel 4's series pits two diametrically opposed experts against each other in a kind of Dogmatist's Smackdown. The notion is that their theoretical differences will be put through a practical trial by combat, with the over-excited suggestion that failure in this duel will actually have some larger consequence than momentary embarrassment for the losing party. In last night's show, Paul, a tough-love personal trainer, and Janet, an alternative therapist who believes that you can brain-train your way to a flatter stomach, were, we were assured, putting "their reputations on the line and their livelihoods at risk".

They weren't, of course, since, like many experts, one of their main skills is the ability to explain why a failure of outcome isn't actually a failure at all, either because their method hasn't been properly applied or because its success can only really be observed over a longer time span. In the short term, though, there was no question that Janet lost, which was hardly surprising since her method consisted of a lot of implausible gobbledegook about "collapsing negative feelings" and "changing the encoded information in your meridians". Paul, on the other hand, did a lot of shouting and swearing, in pursuit of his belief that "people are overweight because they're lazy".

Each expert had chosen their opponent's guinea pig for them, picking from a line-up of obese volunteers in a cruel reversal of playground team selection. Paul got Emma – whose favourite food is her dad's spam-and-egg pie – while Janet got Shareema, who worries that her weight is dragging down her singing career. Along with all the potential trainees they had been described as "desperate to lose weight", though obviously they weren't desperate enough to do something about it before now. Shareema seemed happy that she'd drawn the method that involved relaxing in a chair, while Janet blathered about "finding the off button for the negative chatter", but although Emma looked to have drawn the short straw, she stormed it, losing 22 pounds of flab to Shareema's rather feeble six pounds. Janet – with an audacity that was almost admirable – consoled Shareema with the words "but I have to say you've lost so much weight off your mind". Neither expert could really claim vindication, since it was obvious that Paul's regime would work much better with a bit of gentle encouragement thrown in, while Janet only got the result she did because she eventually adopted a Paul-like approach to her client's over-upholstered rear-end. Where Paul had gone in for "kicking ass", Janet organised a "mind boot camp" so that Shareema could get "the rocket up her backside that she needs". And two months on, neither woman was willing to be weighed for the update credit line, which suggested that no method in the world will work unless you stick at it when the cameras have gone.

The Great British Bake-Off is a gladiatorial combat between 10 of the "country's top amateur bakers", conducted under the scrutiny of Mary Berry, the queen of Aga cookery, and the master baker Paul Hollywood. Each week, the programme's marquee heads for a different corner of the British isles and different baking challenge, and they kicked off with cakes in the Cotswolds. It's essentially a three-tier construction, interspersing layers of practical cookery challenge with a filling of lightly whipped culinary history. And it's quite moist and moreish really – the sort of thing that makes you think you might well come back for another slice. It helps if you're interested in cooking, obviously, but even if you aren't there's a certain psychological curiosity in the varied approaches to this most cosy form of cooking. David, for instance, bakes rather like Paul does press-ups, with a no-quarters perfectionism that was a tiny bit scary. Some of the other competitors clearly possess an over-developed feeding instinct, having honed their craft by making little treats for the people who work in their office. The drama is modest. Lea was having problems with her ganache last night, while Mark had so anxiously supervised the baking of his sticky marmalade tea loaf that it crumpled in the middle. But the judging is nicely technical, for those who really care, and every now and then you get an instructive little chat with a historian, about the Puritan disapproval of spices or regal influence on the development of the modern wedding cake. One thing is slightly mysterious though; it's presented by Sue Perkins and Mel Giedroyc, a partnership once notable for its refreshing tartness. Here, despite the fact that they've stirred in the recommended measure of both Mel and Sue, that flavour has almost entirely disappeared from the finished product. You get a little hint of Sue – with the odd cheeky ad lib – but Mel is so swathed in standard presentational buttercream that virtually no acid comes through at all. Still watchable, but I'd advise Emma and Shareema (or anyone else on a diet) to steer clear.