There are physical *and* psychological reasons behind this phenomenon.
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You've been there: You had an amazing workout and had no problem eating healthy, well-portioned meals for the rest of the day. But the next day, your much-deserved rest day? You're suddenly ravenous. Instead of that veggie- and lean-protein-packed salad you planned to eat, you can't stop thinking about all the other delicious things you could be noshing on-pizza, burgers, get the drill.

So why is it so freaking hard to stay on track on the days when you're not working out? And is it all in your head, or is something else going on? We talked to sports dietitians to find out.

The Physical Reasons

Long story short, it's ~not~ your imagination playing tricks on you when you feel hungry on rest days. As it turns out, there are quite a few physiological factors that could be at play.

Your hunger hormones are affected by exercise. When you exercise, you create an energy deficit. If you're not eating more to replace that deficit (like when you're trying to lose weight, for example), it's only natural to feel hungry. "Sometimes people may feel less hungry on days when they have heavy training loads due to blood flow being distributed away from the gut into extremities," explains Meagan O'Connor, R.D.N., C.S.S.D., a sports nutritionist for Renaissance Periodization. "When this is the case, the body may regulate itself in the following one to two days post-exercise to compensate for the food that wasn't eaten after exercise to make up for the energy deficit. This means you see an increase in the hormone ghrelin (which makes us feel hungry) and a decrease in the hormone leptin (which makes us feel full/satisfied)."

High-intensity exercise can suppress your appetite. "High-intensity exercise can serve as an appetite suppressant due to the accumulation of lactic acid," notes Edwina Clark, R.D., C.S.S.D., head of nutrition and wellness at Yummly. It can take a while for your appetite to return afterward, which is why you may find yourself eating less in the hours after a super tough workout. Eventually, this effect wears off, and you start to feel hungry again. (So if you work out in the evening, hunger may set in the next day.)

You may not be eating enough before and after workouts. "It can take up to seven to 14 days for a muscle to fully recover after a difficult workout, and this largely depends on the type of fuel you are giving your body," says Amy Goldsmith, R.D., owner of Kindred Nutrition. Your body needs carbohydrates to refuel the glycogen stores used during your workout, as well as protein to assist with muscle recovery. "If you burn calories and strain muscles in a workout and then don't eat enough to assist with healing, not only will you have extended muscle fatigue, but you will also feel hungry," says Goldsmith.

You're focused on strength training. Some types of exercise can make you feel hungrier than others. "Strength training makes you the most susceptible to a larger appetite on rest days because your metabolic rate is increased for about 36 hours after the activity as your body is trying to recuperate the strained muscles," says Goldsmith.

The Psychological Reasons

It's also worth noting that there may be some psychological factors at play here, which of course can vary from person to person.

You may feel more inspired to eat well after working out. "I have had clients tell me that they eat better on days they exercise because they feel they are hitting their goals and they don't want to ruin the work they are putting into exercise," says Goldsmith. Similarly, this means you're more likely to want to go for the junk food on days when we haven't exercised.

You feel like you've "earned it." "Sometimes people believe that they have earned a big eating day because of the previous day's training efforts," says O'Connor. And depending on your goals, it may very well be true that you need to eat more the following day because of your workout, but talking about food in terms of "earning" and "deserving" it can lead you down a slippery slope of black-and-white thinking.

How to Deal

If you don't have a specific caloric or macro goal for the day, then the solution to being hungry on a rest day is simple: Eat more. "If you're someone who is trying to maintain your weight, then you should eat more to make up for the calories you burnt off after intense exercise," says Natalie Rizzo, R.D., an NYC-based sports dietitian. "If not, you will lose weight unintentionally, which can hinder your athletic performance."

But if you do have a reason to limit your food intake on rest days-i.e. weight loss, body recomposition goals, or something else-here are some strategies to try.

Fuel your workouts properly. "Look at what you are eating on the days you are exercising and pay attention to the macronutrients consumed," says Goldsmith. A person who is undereating carbohydrates on exercise days will have a significant increase in ghrelin, and therefore be hungrier the next day, she explains. And if you're not eating enough protein or fat, you may never feel satiated. (Need a little extra help here? These are the best pre- and post-workout snacks for every workout.)

Be sure you're hydrated. "You should also be sure to get adequate fluids (especially water) throughout the day," says O'Connor. "Oftentimes people may feel like they are hungry when in actuality they simply have not had enough fluids that day." (Here are a few other sneaky signs that you may be dehydrated.)

Gauge how hungry you really are. "If the hunger is just a feeling that you could eat and you're thinking about craving something, that's mostly psychological," says Goldsmith. "If you're hungry to the point that you would eat anything put in front of you with no questions, that is true hunger. Never allow yourself to go to the point of hunger where you can't focus, are dizzy, have a headache, or feel faint."

Distract yourself. If you decide that you're not truly hungry but more just thinking about food, try doing something else for a while. "When feeling hungry on rest days, try staying active in non-exercise ways, such as hanging with family and friends, or running errands," suggests O'Connor. "Sometimes we just 'feel hungry' on non-training days because we are bored." (BTW, rest days aren't about sitting on your butt and doing nothing.)

Be strategic about your rest day meals. "Make sure to get protein in each of your meals, never going longer than five hours at a time during the day without it," says O'Connor. "This will keep a constant stream of amino acids in your blood to not only maintain your muscle mass but to help you feel satiated throughout the day."

Consult an expert. Eating for a specific goal can be complicated. Sometimes, you just need a little help figuring it all out. Check in with a dietitian about your rest day hunger pangs, and they're bound to have even more suggestions for how to overcome them.