In which I learn that going on holiday in France and Spain is not conducive to weight loss, writes Sarah Vine

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I started out well. On the ferry from Portsmouth to Santander I availed myself of the excellent buffet, judiciously avoiding carbs, lactose and gluten. So basically, smoked salmon. Which was fine, quite nice actually. There was some salad too, and fruit for afters. About half-way through our 24-hour crossing, my sea sickness kicked in, so that took care of the rest of the journey. As we drove off the ferry, I felt smugly saintly.

The trouble began on land. The thing about Spain is that they don't really do vegetables. Or salads. Bread is a staple of every meal. Things are deep-fried and swimming in fat. Even a simple dish of garlic prawns comes saturated in fat. As for potatoes, they are everywhere.

Within 24 hours I was extremely hungry. Adhering to a strict no dairy, no gluten, no grains, no carbs regime in Britain is easy. Every supermarket has a "free from" section. There are plenty of substitutes, readily available. In Spain, it's considered positively eccentric.

MORE GLOSS: Amelia Freer's healthy spicy feta pepper recipe

In the Picos de Europa, a magical little mountain range in the North West of Spain, the Hotel del Oso came to my rescue. It's not an especially fancy place, but the food is incredible. On the menu, consommé and grilled sardines: perfect. And delicious. The following day I had sopa de gallina (chicken soup) and an extraordinary bean stew. I felt happy: good food, according to all Amelia's rules.

Back on the coast, in the heart of Basque country, my family tucked into delicious steaks and lavish helpings of patatas bravas while I stuck to plain fish, with the odd green bean for roughage. Spanish puddings are almost entirely milk based, so they were verboten. As was the vast range of cheeses on offer. I consoled myself by sipping very cold, very dry sherry and eating salty almonds. Those, at least, I was allowed.

MORE GLOSS: Should you go gluten-free?

And then we crossed into France, and my resolve faltered. The bustling 17th century city of Bordeaux is a hotbed of culinary temptation. And wine, of course. Lots and lots of delicious wine. A most exquisite torture. And, I'm afraid, it wasn't long before I fell off the wagon quite spectacularly. A bit of a problem with a rather fine, fresh white and a rather irresistible chocolate pudding (why is it always chocolate?).

As I write, I am in the Loire Valley, staying in a magnificent old hotel. Our room is carved out of the rock. I have been given a welcoming present of champagne and fudge. Somewhere in the kitchens, a chef is preparing a menu degustation. No doubt it will involve cream, fat, gluten, and barrel loads of carbs and sugar. Still, it would be rude not to…

Click here to read  part one  and  part two  of Sarah's weight loss journey.