Scientists are uncovering how our metabolic response to foods affects our cravings, hunger, and food intake.
Two very interesting studies were published this year, one looking at how carbohydrates affect hunger and food cravings, and the other evaluating how post-meal dips in blood sugar predict when and how much we will eat later on. Understanding how different foods affect hunger and food intake is extremely relevant to body weight control and overall metabolic health, as cravings can often pose a threat to even the best of your intentions.
The first of these two studies was a randomized controlled trial where 72 participants initially lost ~12% of their body weight during the 10-12 week “run-in” phase before being randomized into one of three diet groups:
Low carbohydrate (20% of calories from carbohydrates)
Moderate carbohydrate (40%)
High carbohydrate (60%)
Calories during these test diets were adjusted to each individual in order to maintain their weight loss. After following their allocated diet for 14-20 weeks, each participant underwent brain imaging (MRI) scans before and 4-hours after a meal to assess brain blood flow. They also completed a food craving questionnaire.
The results showed that the high carbohydrate group had higher brain activity in regions of the brain associated with addiction and cravings, in both the fed and fasted state. The food questionnaires, however, revealed no significant differences in subjective hunger between the groups, so whether or not this effect is relevant to real-life requires further investigation.
What these findings do suggest however is that high carb diets both acutely and chronically may impact our reward systems in a way that promotes increased cravings and overeating. Similar results have been seen with shorter-term studies, so this is a really important finding because it demonstrates that high-carb diets may have effects in the long term as well.
As the senior author of the study framed it on Twitter: “A high carb diet stimulates brain areas in ways that could increase hunger and food cravings, and adversely affect metabolism. If true, then a focus on “calories in, calories out” to lose weight (without taking into account the type of calories) may set the stage for failure.” – David Ludwig, PhD
The second study published in Nature Metabolism adds a bit more to this story. This clinical trial looked at the CGM (continuous glucose monitor) data from over 1,000 participants over 14-days. The participants were given standardized breakfasts each day of the study that varied in macronutrients (high carb, high fat, high protein, etc.) and asked to fast for the next three hours but were free to eat whatever they wished afterward. Each participant recorded their perceived hunger and alertness within the two-to-three hours following the standardized meal.
The researchers were interested in seeing how the rise and fall in blood sugar would affect perceived hunger and how much the participants would eat for the remainder of the day.
Interestingly, it was the glucose dips in the 2-3 hour period following the standardized meal that were correlated with subsequent hunger and food intake; not the rise in blood sugar within the first 2-hours. The results showed that the greater the dip in blood sugar after eating, the greater the hunger, the earlier they would eat, and the more food the participant would eat at their next meal.
This is the largest study to date demonstrating the role of blood sugar in regulating hunger and caloric intake, and in a real-world situation to boot, as the study took place in an at-home setting. Of the standardized meals, the oral-glucose tolerance test (OGTT) caused both the greatest rise and dip in blood glucose (19% below baseline) which isn’t surprising considering this is essentially 75g of pure sugar.
However, there are many common foods that act similarly to an OGTT such as sugar-sweetened beverages and candy. So, what we can take away from this study is that the consumption of foods that trigger a large rise and fall in blood sugar can cause us to over consume calories over the course of the day and gain weight. Importantly, this research also suggests that by using real-time glucose data, we can personalize our food environment to promote greater satiety to support healthy body weights and thus metabolic health.
Together, these two studies suggest that our hunger and cravings are directly affected by the types of food we eat and how our bodies respond to them. Diets high in carbohydrates, and more specifically, high glycemic foods (foods that create a much larger blood sugar spike), may increase hunger, food cravings, and promote overeating. On the flip side, these studies suggest that by focusing on food quality, we may be able to better support intuitive eating for weight management instead of simply focusing on cutting calories.
See you next time,
Science Writer at Zero