Norman Swan: A lot of people are on low carb diets, but they mean different things to different people. Some people have a low carb diet where there is a lot of fats, a lot of animal protein or fat. Some people have more of a plant based low carb diet. And so the question is, which are better for you, particularly when you look at weight loss? And this study took data from massive studies, you know, thousands of people, they were health professionals and nurses who'd been followed for different health conditions for many, many years. And they were looking at weight change. Now, Tegan, this is not weight loss, because sadly, as you know, as we get older…well, you don't know, you're slim and lithe...is that we all put on weight as we get older. The question is, are we putting on weight faster or slower, and it really looked at the trajectory of our weight gain over time, relative to the kind of low carb diet we were on. And one of the people on this study was Qi Sun who's Associate Professor of Nutrition and Epidemiology at Harvard School of Public Health.
Qi Sun: I found really contrasting effects on body weight, depending on which type of low carb diet our participants consumed. For example, when we look at the low carb diet that is dense in animal protein and animal fats, we found consuming this kind of low carb diet is actually associated with faster weight gain. In contrast, if we look at the low carb diet that emphasised plant protein, vegetables oils and so forth, those actually are associated with slower weight gain.
And we also examined two other types of low carb, one we called healthy low carb, which means this low carb diet emphasises carbohydrates from whole grains and also plant proteins and also vegetable oils. So this is the best version of the low carb diet and associated with less weight gain in comparison with other low carb diets. But the last one is the worst, called unhealthy low carb diet. So this diet emphasises carbohydrates from white bread, from sugar sweetened beverages, emphasises protein from animal products, and also emphasises animal fats. This diet is actually associated with faster weight gain.
Norman Swan: So even if it's low carb, the quality of carbs was low, and you were getting more animal proteins, animal fats.
Qi Sun: That's absolutely correct. But I think there's an interesting point I want to make that following a healthy, low carb diet, a very healthy vegetarian or vegan diet could fall into this category, however it can still contain a small proportion of animal products. But a diet that emphasises really…if you eat carbs from whole grains, from fresh fruits, vegetables, nuts, and so on as a source and also cooking oil as a source of protein and fat, within that there could be still a small proportion of animal product but it's not emphasised.
Norman Swan: So, let's go back to basics here. When you compare low carb diets with just calorie control or portion control or a Mediterranean diet, do you need to be on a low carb diet to moderate your weight gain as you get older?
Qi Sun: Based on our data, and also the data from others studies, the answer is no, you don't have to focus on a low carb diet. What you should focus on is to improve the diet quality, whether it's a low carb diet, a healthy low carb diet, whether it's a DASH diet, whether it's a Mediterranean diet, those kinds of high quality diets are all associated with slower weight gain. So I think absolutely it's not necessary that you have to eat a low carb diet to achieve weight maintenance or weight loss, you should focus on the quality of your diet. That's the key.
Norman Swan: So the bottom line here really is, yet again, you're showing that if you only focus on one element of your diet, in this case carbohydrates, you could be misled into thinking that you've got the solution to your future weight and health, when you should really be thinking about your diet as a whole.
Qi Sun: Yes, I agree with you, 100%.
Norman Swan: Thank you very much for joining us.
Qi Sun: Thank you for having me.
Norman Swan: Qi Sun is Associate Professor in the Department of Nutrition and Epidemiology at the Harvard School of Public Health.
