Last Night's TV: Hairy Dieters: How to Love Food and Lose Weight, BBC2 / The Churchills, Channel 4

The Hairy Bikers have been putting me off my food for a couple of series now, but until last night I don't think it was intentional.

Strictly speaking, they're not really trying to get us to stop eating now, only to eat a bit less and stop cooking with butter. Because the Hairy Bikers have noticed – or someone has noticed for them – that their brand of gleeful, full-fat gourmandising sits a little uneasily with the growing obesity problem. They are, sadly, all too representative of a hefty wedge of their audience in being decidedly over-upholstered. Hence, Hairy Dieters: How to Love Food and Lose Weight, a series in which they will attempt to shed their own excess stones while working up some healthier ways to pig out.

I'm not sure it was entirely wise to start with one last blow-out, gathering the family for home-made chicken kievs and pecan-nut cheesecake, a feast that only reinforced the dangerous association between saturated fat and eating pleasure. But once that odd misstep was over this turned out to be a rather more serious programme than you might have anticipated. The grating perkiness of the double act disappeared altogether at one point when Si revisited his primary school to recall a scalding moment from his childhood, when a teacher boomingly announced that he was on a diet in front of the whole school. "I've carried round that comfort-eating little lad for too long," he said, scratching his beard in a way that seemed designed to stave off tears.

You can't really claim to be a fully fledged BBC presenter these days unless you've been pushed through some form of high-technology scanner, so they went off to a research institute next to have their body fat assessed, an equally sobering moment for both men, who knew perfectly well that their skeletons were still in there somewhere but hadn't quite absorbed how clagged by fat they were. The doctor set them both targets for weight loss to which they added their own less quantitative incentive. Dave wants to be able to walk into a Paul Smith shop and buy a suit off the peg and Si just wants to be able to take his shirt off in public without cringing. Dave, perhaps anxious that two goals isn't enough, has also promised to pay his step-daughter £500 if he can't get a favourite pair of jeans on at the end of three months.

They then enlisted some other wannabe losers to bolster their willpower and organised what appeared to be yet another final feast before the fast – the trick on this occasion being that their lasagna was a cunningly low-fat affair, in which the "pasta" was boiled leek and the bechamel had been thickened with cornflour. I don't know what it tasted like (the guinea pigs were all politely enthusiastic on camera), but it sounded to me as if it would successfully persuade almost anyone to cut down their portion size. Still, the cause is a good one. Paradoxically it's a while since the Hairy Bikers have been this palatable.

David Starkey began the second part of his series The Churchills with another arresting bit of detail: the moment, in pre-war Munich, when Winston came within a whisker of meeting Hitler. The date had been fixed by Putzi Hanfstaengl, a Harvard-educated art dealer, but Hitler didn't turn up for tea, figuring that Churchill wasn't powerful enough to bother with. There's an almost comic vanity to Starkey's thesis at times – its insistence that the study of history is the secret elixir that transforms Churchill from mere politician into super-hero statesman. But, as old-fashioned as it is, it's also very engrossing narrative history, braiding the careers of the Duke of Marlborough and Winston in provocative and often illuminating ways. Perfect as a palate cleanser after all that sport.

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