Happy Saturday! Today I have a video for you where I go over a scientific study on what happens when people overeat sugar. Specifically, how much sugar you can turn into fat (through de novo lipogenesis), and whether sugar makes you fat.
This study compares lean and obese participants in terms of their de novo lipogenesis (DNL), which is the process of converting carbohydrates into fats in the body. The researchers fed people 3 diets for 4 days each: a control diet to maintain their weight, and two overfeeding diets. The participant were in a calorimeter room during these diets to measure exactly what they burned off, and their activity and rest was controlled. The control diet was a pretty normal, Western-style diet: about 50% carbs, 40% fat, and 10% protein.
In both overfeeding diets, they were overfed by 50%, half of which was fat (butter and oil added to meals), and half of which was sugar (sugary drinks). In one overfeeding diet, they were overfed with sugar in the form of glucose, and in the other diet, they were overfed sugar in the form of sucrose. There were no differences in the outcomes by the type of sugar, so I don’t talk about that in the video.
The researchers looked at what happened to the sugar especially: how much of it they burned off, how much of it they turned into fat, and how much it contributed to body fat gain. They also looked at whether fat or sugar leads to more increases in DNL, how the overfeeding diets affected insulin and blood sugar, and more. I spend most of the video going over the results, and what they mean for you!
Here’s a link to the study: https://academic.oup.com/ajcn/article/74/6/737/4737416
Extra science notes
Here are some notes on parts that I cut out of the video, since they’re more for people specifically interested in science!:
- The effect of increased energy expenditure with the overfeeding diets wasn’t statistically significant, but there was a consistent increase in all 4 overfeeding groups (lean and obese, sucrose and glucose). Given the small number of subjects, it is likely this effect would be significant if more subjects were included. There are also other studies finding this increase in metabolism with increased food intake, which I plan to make another video on too! (e.g., https://www.nature.com/articles/ijo2012202)
- Fat balance and carbohydrate balance each explained 43% of the variance in DNL. Therefore, it appears that overeating generally rather than solely carbohydrate intake may be responsible for increasing DNL.
- The numbers on the plot are in kilojoules, which is a standard scientific unit for energy. For the video, I converted it to calories to make it more applicable. If you look at the paper yourself, note that many of the numbers are in kJ (or grams, for macronutrient balances) per 96 hours.
- The paper was funded by sugar interests, which would be a big problem if it were the only paper showing low rates of DNL like this, or if their main goal was to show how low DNL is. Luckily, there are many other studies showing similarly low rates of DNL, but I chose this one as the example for this video because it was a nice method, published in a top nutrition journal, and made the numbers available. The main goal of this study (aka what the sugar industry wanted) was actually to test the differences between sucrose and glucose in DNL–they found no effect. Also, they focused more on how DNL doubled than how low it was, suggesting their goal wasn’t to push a low-DNL sugar agenda.
- Here is another paper reaching the same conclusions, from Berkeley and not funded by the sugar industry: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC185982/