Grandmothers were big on food rules such as 'eat your greens, you'll grow big and strong' or 'eat your crusts, they'll make your hair curly'. These days, it's not so much grandmothers as health writers and reporters who are full of food rules. The trouble is, they change almost daily. Who do you believe? Common sense is the best teacher, says Claudia Del Vecchio, chief nutritionist for the Kosmo chain of health cafes, who is visiting Hong Kong this week. The good-foods, bad-food rules are not nearly as important as simply keeping your system ticking over by giving it the right fuel - a good range of foods - and around 2,000 calories every day. Unfortunately, what most of us do is eat 700 calories some days - six cups of coffee, a drink, a couple of biscuits and a snack - and 4,000 the next, with a big day at the buffet and a night out drinking. It's a big task for the most flexible metabolism. And in Hong Kong our immune cells are constantly demanding that our metabolisms supply them with extra resources - energy, anti-oxidants and more - to combat the pollution and viruses assaulting our bodies daily. 'It's about bringing the simple things back. It's all about balance and moderation,' says Del Vecchio. 'If you eat too little and drink coffee all day long you build up the caffeine levels to a point where by the evening you are irritable, have a headache coming on, and can't relax or eat properly. Caffeine in moderation can be very good - it opens up the mind, gets you started. But too much and you are stressed,' the American nutritionist says. And before long you may have a stress-induced illness. The other end of our chaotic eating patterns is over-indulgence. While many of us under-eat and overdose on caffeine during the week, at the weekend people try to make up for lost time by overloading on sugar, fats and alcohol. 'On weekends you go to a buffet, load up on sugars, the bad fats, have dessert, a few beers, no exercise, a few more beers. You wake up the next morning feeling terrible,' Del Vecchio says. That describes the week a lot of people in Hong Kong are living. But given the pressure to get your work done, to take only five minutes to grab a coffee and get back to your computer, and the release many people need when the weekend comes around, how can we make theory and practice work here? 'Those few beers could have been just right,' says Del Vecchio. It is the next two and the two or three or four after those that cause the problem. 'These foods are good for you in moderate amounts. It's simple. But it is not just the weekend overload. If the food restriction and time restriction were not going on all week, the weekend overload wouldn't be so inevitable. We go from hell to heaven and hell again in less than 24 hours. And our bodies are not made for this kind of battering.' So is there a magic formula? 'No!' she says. 'Eat balanced. Don't make your blood sugar go up and down. 'By reducing the stress on your system by such erratic patterns you automatically increase the strength of your immune system. And in Hong Kong you need a strong immune system all year round, so eating well and wisely is not something any of us can afford to ignore. 'If it's cold out, you put on a coat. But what are you going to do if you are going into this environment,' Del Vecchio says, gesturing to the traffic-choked street. 'Look for food less refined, less degraded. Don't eat food that has a lot of added sugar and fats. You want food in the whole form, not processed. Buy fresh food, don't leave it in your refrigerator for a week. Eat more plant-based foods - they are higher in antioxidants - and eat fattier fish.' Del Vecchio also believes we need to take vitamins C and B complex because we fight to get enough of these. And you must try to stop making your metabolism do the equivalent of a marathon every week.