Food choice and food reward during 60 days of head-down bed rest with exercise and artificial gravity countermeasures in healthy men: The BRACE study
In a 60-day head-down bed rest study simulating spaceflight, healthy men experienced a spontaneous decrease in energy intake and specific shifts in food preferences and reward, but neither exercise nor artificial gravity countermeasures significantly altered these dietary responses.
Original paper licensed under CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). This is an AI-generated explanation of a preprint that has not been peer-reviewed. It is not medical advice. Do not make health decisions based on this content. Read full disclaimer
The Great Space Diet Mystery
Imagine your body as a high-performance car. Usually, the driver (your brain) and the engine (your muscles) have a perfect conversation: "I'm running fast, I need more fuel!" or "I'm parked, let's eat less." This conversation keeps your weight and energy levels in check. But what happens if you take that car apart, lay it flat on its back, and turn off the engine for two months? Does the driver still know how much gas to put in?
This is the question scientists are asking about astronauts. When humans float in space, or lie flat in a bed to simulate zero gravity, their bodies go through weird changes. Their muscles shrink, their bones get weaker, and their sense of taste can get a little fuzzy. Scientists call this "microgravity" (or the feeling of it), and they worry that astronauts might stop eating enough, or start craving the wrong things, which could be dangerous on a long trip to Mars. To figure this out, researchers use a clever trick: they have healthy people lie in bed with their heads tilted slightly down for weeks. This tricks the body into thinking it's floating, even though it's just on Earth. The big question is: if we make these people exercise while they lie there, will it help their brains remember how to eat normally?
The Experiment: Lying Down for 60 Days
In a study called the BRACE study, scientists put 24 healthy young men into a very strict "bed rest" mode for 60 days. Imagine being grounded for two months, but instead of just sitting on the couch, you have to stay in bed, eat, shower, and even use the bathroom while lying down with your head tilted down. It's like a very long, very boring nap where you aren't allowed to stand up.
The researchers split these men into three groups to see if different "countermeasures" (tricks to fix the body) would help their eating habits:
- The Control Group: Just lay there and do nothing special.
- The Exercise Group: Did intense cycling while lying on their backs.
- The Super-Exercise Group: Did the same cycling but also spun in a giant centrifuge to create "artificial gravity," trying to trick their bodies into feeling like they had weight again.
Before and after the 60 days, the scientists tested the men's eating habits in two fun ways. First, they threw a massive "all-you-can-eat" buffet where the men could grab whatever they wanted. Second, they used a computer game called the "Leeds Food Preference Questionnaire" to see what foods the men liked (how tasty they thought they were) and what foods they wanted (how much they felt a craving for).
What They Found: The Body Gets "Unresponsive" with Food
The results were surprising. First, the scientists found that neither the cycling nor the artificial gravity changed the men's eating habits. Whether the men exercised or just lay there, their brains and bodies reacted to the bed rest in the exact same way. The exercise didn't "fix" the eating problem, though the study was small, so the scientists can't say for sure that exercise is useless forever.
However, the bed rest itself caused some very specific changes in how the men ate:
- The Buffet Shrank: After 60 days, the men ate 264 fewer calories at the buffet than they did before. They didn't just eat a little less; they chose smaller meals overall.
- The "Protein" Drop: Even though they lost muscle mass (which usually makes you crave protein), the men actually chose less protein relative to carbs and fat. It's like their bodies forgot that they needed to repair their muscles.
- The "Color" and "Fiber" Crash: The men's brains stopped finding colorful foods as exciting. Their "liking" for high-protein foods and colorful foods dropped. Also, their "wanting" (the deep craving) for high-fiber foods (like veggies and whole grains) disappeared.
- The "Junk" Shift: Even though they ate less total food, the food they did eat was denser. They chose more high-fat, high-sugar, and high-carb foods. They also picked more "finger foods" (foods you can eat with your hands) and "non-habitual" items (foods they didn't usually eat).
Why Did This Happen?
The scientists think the men's brains got a bit confused by the boredom and the strange environment. When you are stuck in bed for two months, eating the same few meals over and over, your brain might start looking for a spark. That's why they reached for the colorful, sugary, or crunchy foods—they were trying to find something new and exciting in a very dull world.
The study suggests that when your body is "unloaded" (not fighting gravity), your internal fuel gauge gets messed up. You might eat less, but you might also crave the wrong things. The exercise didn't seem to stop this from happening, at least not in this short 60-day test.
The Bottom Line
So, if you were an astronaut heading to Mars, lying in bed for two months would likely make you eat less, crave sugary and fatty snacks, and lose interest in healthy, colorful, or high-protein foods. Doing exercise while you lie there didn't stop this from happening in this study. The scientists say we need to do more research with bigger groups to be absolutely sure, but for now, it looks like space travel might require some serious menu planning to keep astronauts' brains happy and their bodies healthy.
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