Sometime back in the early 1990s or thereabouts, Dolly Parton was being interviewed by the famous BBC chat show host, Michael Parkinson. When asked about what diet she used to keep her figure, she replied: “Honey, if you want to lose weight, get your head out of the slop bucket”. In other word, just eat less. No truer words were ever uttered in the vast realm of advice on dieting. This year we have seen a number of scientific papers published on sugar sweetened beverages, some designed to boost weight gain and some designed to induce weight loss, all adding to the belief that sugar sweetened beverages are both the cause and the cure for modern obesity. A recent paper from the Department of Nutrition at Harvard will help put things in perspective, but only for those wishing to have an accurate perspective.
The first  of the sugar papers looked at four groups each given 1-liter of a beverage per day for 6 months. Group 1 receiver a liter of regular sugar sweetened Coke. Group 2 were given a liter of semi-skimmed milk with an approximate equal calorie level to the Coke. Groups 3 and 4 respectively received 1 liter of diet Coke or water. According to the authors, the consumption of the energy-containing beverages led to a compensation effect with a reduction in the intake of other foods and no overall change in energy intake. No dietary data are provided in the paper but 1 liter of regular Coke would have diluted out its equivalent caloric value from all other foods, leading to a reduction in the intake of the latter by 430 calories per day. This Coke group showed a significant accumulation of fat in the liver compared to others but we will never know if it was due to the absurdly high total intake of sugars (about double the normal according to my calculations) or to a reduction in the intakes of micro-nutrients associated with 430 less food than normal every day. Coke for example, does not contain, the B-vitamin riboflavin, but low riboflavin status will lead to increased blood pressure, and the authors did see a rise in blood pressure with regular Coke.
So, 1 liter of Coke per day did not lead to weight gain ( for example a 1.3% gain with Coke and a 0.8% gain with water). However, two studies reported in the New England Journal of Medicine show that if sugar sweetened beverages in children are replaced with a calorie free version, then weight loss does occur . These studies will be widely cited as evidence that sugary drinks cause obesity. In fact, these studies simply show that if you do as Dolly Parton says, and simply eat less, you will lose weight so the weight loss could have been with any caloric source, not just sugar-sweetened beverages.
Which brings me to the Harvard paper . This study (a subset of a larger dietary intervention) looked at how variation in the distribution of calories in a weight loss regimen influenced weight change and also changes in body composition. Four dietary treatments were used and an energy deficit of 750 kcal per day was the target for each participant. The diets varied the level of fat, protein and carbohydrate. At 6 months, the average amount of fat lost was 4.2 kg and the loss of lean tissue was 2.1 kg. About half of this fat loss was due to loss of fat from the abdominal fat with about a third lost from subcutaneous fat. Only 0.1 kg of fat was lost from the liver but this represented a loss of 16% of liver fat. There were no differences in any of these measures according to the composition of the weight reduction diets, again, upholding the Dolly Parton rule.
In summary, the first study tells us that if you oblige subjects to eat a 1-liter bottle of regular Coke every day, you won’t gain weight because you reduce your intake of other foods keeping energy intake constant. The second tells us that extracting calories from children’s diets will lead to a weight loss, in this case using sugar sweetened beverages as the target food. The third tells us that Dolly Parton was correct. It really doesn’t matter what the composition of your weight reducing diet is so long as the caloric restriction operates.
So for what its worth, here are my basic rules about successful dieting:
1. Never start a diet until you have though about it long and hard given that the relapse rate of weight loss is so high.
2. Never start a diet until you have built physical activity into your daily routine. Physical activity will reverse the negative effects of obesity such as poor glucose management, higher blood pressure and elevated blood lipids.
3. Don’t diet on your own. Join a weight loss group and get the benefit of the social network of dieting and maintaining weight loss.
4. Heed Dolly Parton and just eat less and eat according to your preferences