Torwen:
Hi and welcome back to the Ideal Nutrition podcast. Hope you’ve all had a fantastic week. Today we’re going to talk about the impact of carbs before bed and whether they can help sleep. So, we’re going to cover mechanisms, timing, the glycaemic index to consider, the pros and cons, and how you could put this into practice.
Aidan:
So, we’re going to start with the mechanisms. There are so many mechanisms, which is one reason why I prefer to focus on outcomes. I think it’s still worth us talking about them. There are two main mechanisms most commonly discussed. The first is the tryptophan and serotonin pathway. That’s based largely on the logic that carbohydrates increase insulin.
This helps more tryptophan cross the blood-brain barrier and boosts serotonin and melatonin production. Those link directly to sleep quality and onset. That’s one of the mechanisms proposed. The other is blood sugar regulation. The logic is that stable blood sugars may reduce night-time wake-ups. For example, if somebody had a hypo, that’s more likely to lead to them waking up. On that topic, very low-carb intake or a long fast before bed could lead to disrupted sleep through that mechanism.
A little note I want to add on those mechanisms is that theory can sound promising. The practical nature isn’t always as promising. For example, somebody might say, eat X food, it contains melatonin, therefore it helps you sleep better. There’s so much to unpack there. One is that the amount of melatonin in most foods is very minimal, and it’s not really practical. The second is if you look at research on melatonin, it does help sleep.
But, directly supplementing melatonin on average helps by about six minutes. I haven’t put this one in the show notes, but I’ve seen that research. So if we had a very small increase in melatonin due to food, how much difference does that make? That’s why I want to talk about the many proposed mechanisms. I also like focusing on outcomes rather than saying this increases melatonin, therefore it should help.
Torwen:
And, I guess, the studies on the effect of carbohydrates specifically have mixed results. We know that whether it’s complex or low GI carbs has different results. One of the most discussed studies I found is by Afegai et al. They looked at a high GI meal of jasmine rice around four hours before bed.
It significantly reduced the time it took to go to sleep. A few caveats matter here. There were only 12 people in this study. Yes, it could be promising, but that’s not a huge sample size. The meal distribution was interesting as well. So, it was 90.4% carbohydrate, 8% protein, and 1.6% fat. That’s not your typical dinner before bed, if we’re being honest.
Aidan:
We’ve done it again. We’ve got the same study again. That’s exactly right. I saw a lot of people commenting on this topic. They pointed out that sometimes you see benefits, but the practical meal is heavily skewed towards carbohydrate. It’s not really a normal meal. Have you got any other research you want to talk about or any other thoughts?
Torwen:
I do, but it looks more at the opposite and what can cause insomnia. So, I’ll let you take it away first.
Aidan:
Yeah, I’ve just got some other thoughts. I think eating too much food close to going to bed could be an issue for reflux. I haven’t gone deep in the research on this, but it seems well documented. It does reduce sleep quality if somebody has heaps of food right before going to bed. Eating too far from bed could have implications for blood glucose regulation.
That’s similar to the extended fasting thing I mentioned. Something I found interesting is there isn’t as much good research comparing timing as I would like. I see a lot of people talk about rules like stop eating or stop drinking water three hours before bed. Stop eating two hours before bed, and so on. I thought there’d be heaps of research looking at time. There isn’t as much as I hoped for.
Torwen:
Yeah, I found the same thing. There was nothing super clear to say what time frame. That specific study was four hours. Potentially it makes sense to have a decent carbohydrate meal three to four hours before sleep. For most people that’s dinner time. But, given you’re normally having more protein, we know tryptophan uptake can reduce if protein in the meal is higher. So, if we say that, maybe it makes sense to have a snack after dinner. Closer to bedtime with just carbohydrates.
Aidan:
Yeah, that was one of the most practical recommendations I’ve seen for years. It’s a small carbohydrate snack. A high GI option could potentially help as well. It’s interesting there isn’t heaps there. There was a lot on the amount of carbohydrate and the quality of carbohydrate. It could be skewed by healthy user bias.
There was a lean towards lower glycaemic index carbohydrates linking with better sleep. If somebody on average eats lower glycaemic index carbohydrates, do they have more micronutrients coming in? Do they have a better fibre intake? There’s a lot in there. It’s worth noting that comparing total carbohydrate intake across the day shows some positive stuff too.
Torwen:
The one I looked at was in a specific population, a prospective study on postmenopausal women. Overall, higher GI diets associated with increased insomnia incidence. High fibre fruits and veg didn’t have this effect. They are related to reduced incidences of insomnia. That makes it easy to make an overall recommendation. Generally, we should focus on lower GI carbs. Think starches, whole grains, fruit, and veg to help reduce insomnia.
Aidan:
Where do we want to go next with this?
Torwen:
Potentially, the amount of carbs or how much we should look at?
Aidan:
Yeah, I don’t have heaps I want to go with that. There was a little looking at lower-carb versus higher carb diets. One massive review found higher-carb diets tended to improve REM sleep. Low-carb diets tended to improve other stages of sleep. That’s not as great as I wish. It seemed each had different benefits. That leans back to personal preference, based on that, I would say.
Torwen:
Just for anyone listening, we know that in REM sleep your brain is more active. Your brain relies on glucose for fuel. That’s why it makes sense that when you have more carbs, your brain is more active. You enter REM sleep more easily as well.
Aidan:
Could there be downsides of adding carbs before bed?
Torwen:
I think so. Let’s address a common misconception. People say carbs cause fat gain, which creates fear around carbs. People bring this up. We know that isn’t directly the case. Fat gain links primarily to total calorie intake rather than having some carbs before bed.
Aidan:
This is something I’m not proud of but there’s a research review I’ve paid attention to and read every copy of. I’ve spent more time than I’m proud of on this. The review goes through major nutrition studies as they come out. It’s in real time. It’s almost like nutrition history. Something I found interesting over the years is that every month there’s a study on meal timing and body composition. The reviewer takes everything seriously and unpacks each study in isolation.
They try to explain why the findings were what they were. They then put them in the context of the overall research. Every month it seemed like having carbs late in the day is bad. Or that you should avoid carbs earlier in the day, or whatever. Each month looked a bit different. Then you zoom out and balance the research. It’s so clear that it doesn’t matter. It’s your total intake. That said, if you try to avoid carbs after 5 pm, what will you do? You’ll probably reduce your intake of carbs and calories.
That could lead to fat loss. We see this in many other areas of nutrition. For example, if somebody takes up intermittent fasting, they reduce their eating window. Almost every randomised controlled trial on intermittent fasting finds people lose weight. They eat fewer calories. If you restrict how often you can eat, it typically reduces calories.
Torwen:
It makes sense that if you want a calorie deficit and to lose weight, maybe don’t include this extra snack. You’d likely prioritise carbs at other times across the day. Maybe this doesn’t apply completely if the sleep improvement is only marginal.
Aidan:
I would agree. That’s exactly right. Because it’s such a low priority thing and the research is mixed, how much does this matter? I don’t think you should change your overall diet noticeably by adding a bunch of extra carbs. If you’re in a position where it makes sense, that leads to when it makes sense. I’ve got two categories.
One is if you have poor sleep, whether insomnia or just suboptimal sleep. It could be worth experimenting and trying something new. I think it’s worth it in that situation. The other is if you’re an athlete wanting to replenish glycogen stores. At minimum, it’s not making sleep worse. It might help. It’s another window to replenish glycogen for the next day’s training.
Torwen:
Especially if you’re an athlete with higher carbohydrate requirements and you train early in the morning. And you know you need those stores ready for the next day. Maybe you don’t have much time to have carbs in the morning.
Aidan:
Practical thoughts?
Torwen:
If we summarise what we said, eating carbs three to four hours before bed is a good thing. We could recommend smaller carbohydrate-based snacks one to two hours before bed. They could also have potential benefits.
Aidan:
I’d say so for sure. As we were talking about the research, it seems like carbs in isolation matter here. If you add protein, it can reduce some effects related to tryptophan, if that’s the mechanism. There is a niche option I’ll throw out there. And that is tart cherry juice. Research on tart cherry juice or tart cherry extract is promising for sleep in general. This is one of the few foods that seems to increase melatonin.
Note that alone doesn’t explain the benefits. There are mechanisms around tryptophan. I’m focused on research. The research on insomnia stands out. I don’t know if I’ve added the study in the show notes. I’ve added a blog post, so tart cherry juice is in there. It will feature this research. There was a study on insomnia where people got an extra hour of sleep on average. I think that’s too good to be true. I don’t think that’s super replicable.
There’s enough among other sleep research that I’m convinced it helps. And the mechanisms make sense. Tart cherries are about five times richer in antioxidants than regular cherries. Then you juice them and you can get even more through that. Then you concentrate it down into a 70 ml shot that’s very high in antioxidants and other components. The mechanisms make sense to me. You also get carbs alongside that too.
Torwen:
I was going to add that it’s quite carbohydrate rich too. If we’re looking at this side of things, that can be a positive as well. Anything else you wanted to add?
Aidan:
No, I don’t think so. I think with the tart cherry one that is the most practical way I can think of. Who would I try that with? One, people who ideally have a decent amount of money. It’s not super cheap to do this. Or people who want to optimise a lot of variables, including sleep or recovery in other ways as well.
Torwen:
Amazing. Thank you for listening, guys. This is episode 227 of the Ideal Nutrition Podcast, where we chatted about whether carbs before bed help sleep. We hope you enjoyed this episode. If you did, we’d love it if you could leave a positive review. Thank you.