When I was 17, studying for my A-Levels, I was desperate to lose weight. I was on a home-made, DIY style diet (you know the type, stay away from chocolate, biscuits, cake, crisps, peanuts and anything else with fat or sugar in it) assisted and encouraged by my mum. But revising day-in, day-out was so interminably dull that staying away from the biscuit tin, the chocolate and the snacks to keep me from dying of boredom felt like torture. So I found a substitute which, I thought, was the perfect solution: diet coke. I would make regular trips to the kitchen to get myself a drink, taking my time to pour it into a glass, adding ice and a slice of lemon. I would fill pint glass after pint glass, taking them back to my desk to keep me going for the next hour of pretend application. As you might have guessed, academia was not my thing and the coke breaks provided me with very welcome moments of distraction. In contrast to the hours spent staring mindlessly at my revision notes, making myself those drinks gave me the feeling that I was doing something and the endless sipping kept my anxiety and frustration at bay.
I didn’t lose any weight in those endless months leading up to my exams. Not an ounce. In fact I put on a few pounds, despite days and days of abstention and deprivation and feeling hungry almost all the time. Most days I was very, very ‘good’. I ate meals prepared by my mother; salad and steamed veg, grilled meat and boiled fish. And then the caving for something sweet or savoury would just become too great to resist and I would bake a cake or give in and treat myself to peanuts or crisps. What I didn’t know then was that the no-calorie coke was contributing to my weight gain. The evidence from the studies* I have read suggest that there is a mechanism in our biology which causes the sweet taste of the fizzy drink to increase our appetite. Even though there is no sugar in the drinks, they cause an increase in insulin secretion which results in a decrease in blood sugar and also gears our metabolism to fat storage rather than oxidation, in anticipation of metabolic fuel entering the blood stream. Drinking diet coke before a meal or on an empty stomach means we are likely to eat more as our appetite increases and that our bodies are primed to store our intake as fat. We may think we are doing well by avoiding sugar but in fact the sweeteners appear to have the same effect.
So, the more diet cokes I drank in an effort to stay away from the biscuit tin, the hungrier I became, the more I craved fatty and sweet foods, and the more I ate. If only I’d known.
Diet drinks are not innocuous fillers which help us stave off hunger, quite the contrary. Mislead by their ‘zero calorie’ labels, we tend to think that these drink don’t count, that we can consume as many as we like without it impacting our weight or appetite. Not so. What seems to be the case is that the more diet drinks we have the hungrier we get, the more we eat. Worth knowing I think.
*(Powley and Bertoud 1985; Tordoff and Friedman 1989)