My sister Lara, who’s eight years older, cooked and fed me most of my meals as a child. I remember her daring me to eat raw bacon and other things she was scared to try herself. I think what also helped develop my iron stomach is the loose hygiene in our house. Mum would often pick food off the floor and put it back on my plate.

Soon after I’d joined the Scouts, a scoutmaster challenged us to cook a sausage with one match on the pavement. My first thought was, “One match won’t last long enough”, but then I started thinking about what to light with it. So suddenly I was using my imagination and being resourceful and concentrating on getting it right – all the stuff which since has been a big part of my outdoor adventures.

The dinner table is often where the dramas are. Crown Prince Dipendra [of Nepal] went mad and shot almost all his family during dinner. It felt crazy that for years I’d regularly fought – karate – with this guy at Eton. He’d left, grown up, then I heard he’d killed almost all Nepal’s royal family and then himself.

I went on combat survival training after joining the SAS. I was deposited in the mountains, then chased by dogs, soldiers and helicopters, with a bare minimum of clothing and no rations or water. I found a carcass of a wild boar in the forest. The meat was too rotten but I got marrow out of the bones while on the run.

My dad died when he was pretty young – 66 – and it really rocked me. My parents just didn’t eat particularly good food – all those tins and white bread – and so I started examining my diet. I realised “I’m eating a lot of crap, because no one educated me”. So, aged 30, I started educating myself about healthy food. At 41 I feel better, look better than at 30, or 25, and what’s driving it is I’m hopefully not going to die of heart disease like my father.

I’ve spent a lot of my life out there doing wild food – energy and efficient calories for survival, from grubs, bugs, roots, berries and game. All birds and mammals are edible; I don’t think there’s any exception. The venomous stuff is in glands. The skunk has it in his anal glands, of course, but all the rest is OK.

We don’t say it for snacks or for every meal, but when we sit down for a family lunch we’ll try to say grace, or one of our boys will do it. I wasn’t bought up with grace by my parents, but I think generally in life it’s good to have gratitude as a principle for your kids, when a lot of people in grim times don’t have food. I think it’s a really nice humble thing to do, even if you don’t believe in God.

A cup of tea solves a lot of problems. I like a bit of spruce or pine-needle tea. For President Obama I brewed catnip tea. Anywhere you go in the wild you’d be able to make tea from something. Although deserts can be tricky. Deserts are bloody hard.

For the 50th anniversary of the Duke of Edinburgh awards we set a record for the highest altitude dinner party – at 25,000 feet. We had to have three courses, wear formal dress and toast the Queen, so we did it all in naval officer mess-kit suspended under an air balloon and using supplementary oxygen. I tipped backwards after the last course and there’s a shot of me falling through the sky with my suit tails flowing out. It wasn’t great food and it’s between -25C and -40C up there. But all good fun.

Fuel For Life by Bear Grylls (Bantam Press, £14.99) Click here to order a copy from Guardian Bookshop for £11.99