In truth, I started my weight-loss diet in anticipation of the new year, and am already 5kg to the good. A further truth, however, is that that's a small fraction of the weight I've put on since my svelte mid-20s. I don't really have a goal, unless it's no longer to qualify as "obese."

In line with what Mark Henderson wrote last Tuesday, the chilling fact is that I can look at both sides of my family tree and confirm that many of us must have inherited the version of a gene called FTO that makes us 70% more likely to be obese, and to weigh on average 3kg more than those who didn't; and we probably also have the version of the MC4R gene which adds another 1.5kg.

You have probably done the mental arithmetic that shows that I've already counted the extra weight I owe to the variations in my DNA, and have therefore managed thus far to lose half a kilo. So now I'm on my own, with nothing and nobody else to blame for my extra chins.

Apparantly, the "fat" versions of these genes don't actually affect metabolism, but behaviour. Nobody yet knows exactly how they work. But I have a shrewd suspicion that in my case they work their evil not by conferring a sweet tooth (personally, I usually crave salt not sugar), but by interfering with the satiety mechanism. I really never seem to know when I'm full. Psychologically (it seems to me) this boils down to my eating as though I'm always afraid that famine is lurking just outside the kitchen door.

There is one important aspect of my behaviour, though, that is due to nurture, not nature. I was born during the second world war and brought up to feel that wasting food is wrong. "If it's there, finish it," was the maxim of every war-time mother – and I've always obeyed.

So how have I lost any weight at all?

First, I subjected myself to a completely arbitrary prohibition. I've given up something I love (though not wine, which would be a sacrifice too far). My self-imposed ban encompasses foods that have what I think of as "visible gluten," i.e., I've renounced bread and pasta. This means I'm still eating plenty of complex carbohydrates – rice, potatoes, starchy vegetables – but I don't have any toast to butter or tagliatelle to sauce.

Second, and much more crucial, I've been keeping a food and drink diary, in which I try to record everything I eat or drink, with an estimate of the portion size, along with a note about how much exercise I've taken. This is really painful, as the temptation to fudge the figures is sometimes irresistible, even though I'm only lying to myself.

My alcohol consumption is bad, and obviously got worse over the holidays, though I tried to keep the total nightly wine consumption to about 500ml by drinking better rather than more wine during the season of too much cheer. But 500ml of 12% alcohol by volume wine is still way too much – that's about 6 units per day or double the recommended 21 units per week. It was hard to admit to drinking this much; but it will be even harder to reduce it.

Still, keeping the diary, along with a weekly note of my weight, seems to be doing the trick of motivating me to do what nature and nurture don't incline me to do. I'll simply have to keep going till my genes fit. Any advice for this reluctant, recalcitrant dieter?