TL;DR: Caffeine causes an increase in blood glucose levels and creates temporary insulin insensitivity for ~1.5 hrs after you drink it. If you add simple carbs and don’t move around, extra insulin will be released and you’ll have a bigger “sugar crash” about 2-3hrs after the coffee + simple carbs. (about 7 min read)

Metabolic tips to prevent that post-caffeine crash:

• Move around after drinking coffee; if you can’t, skip sweetening your coffee.

• Replace refined flour snacks with high fiber or protein snacks 30 min before and after to avoid an insulin spike that leads to a “sugar crash”.

• Drink a lot of water to help your system rebalance more smoothly.

Caffeine “wakes you up” by increasing cortisol levels. Cortisol naturally increases in your body overnight, reaching a peak in your blood around the time you wake up. Then, cortisol (should) decrease throughout the day until it is lowest before you go to bed. One of the ways that caffeine “wakes you up” is because it also causes some cortisol to be released into your blood, similar to what naturally happens when you wake up in the morning.

The other way that caffeine “wakes you up” is by blocking receptors in your brain that normally respond to a “sleepy signal”, adenosine. Adenosine has the opposite cycle in your body as cortisol - it increases during the day until it is the highest before you go to bed. Then, adenosine levels (should) drop overnight until they are lowest when cortisol is highest.

Caffeine doesn’t give you energy but it does increase the amount of fuel in your blood that your muscles can break down into energy. You may have heard cortisol called the “stress hormone”. That’s partially true - as just discussed, the levels of cortisol in the blood naturally increase and decrease over the course of a day (24 hrs). This is part of your natural “circadian rhythm” and it’s also why it’s stressful on your body to have an erratic schedule*.

Cortisol is also released when you exercise or have a “fight or flight” response (hence the “stress hormone” nickname). Since your body is moving or is expected to start, the release of cortisol also causes your liver to release glucose (see the post on what your liver does if you haven’t already) and your fat (adipose) cells to release free fatty acids into your bloodstream so that your muscles have fuel to turn into energy for the movement you’re allegedly doing (cue core memory of being at my desk twitching mid-afternoon after a strong coffee and an endless checklist… that counts as moving, right?)

But what happens when you have extra glucose released into your blood and you don’t move around (all twitching aside)?

Cortisol and insulin are frienemies. They both work to help your body maintain balance as your energy demands change throughout the day. Cortisol makes sure you’re ready to run (literally) and insulin makes sure your blood glucose levels (BGLs) don’t get too high.

So, if they’re on the same team (Team Metabolic Balance), why aren’t they friends? Because they compete with each other. In addition to causing your liver to release glucose, cortisol also tries to block the action of insulin. Remember that insulin is a growth factor that tells your cells to take extra glucose out of the bloodstream and store it. It makes sense that cortisol interferes with insulin - you can’t have your liver putting glucose into the bloodstream (cortisol) at the same time it is taking glucose out of the bloodstream (insulin). So if both cortisol and insulin are in your blood at the same time, one of them has to knock it off and stop doing what it’s doing.

While it’s true that you cannot outrun your problems, your body does make it possible for you to try. Cortisol wins this match-up: it’s really important that your muscles move faster when you need them to. So cortisol blunts insulin’s ability to lower your BGLs. This means your muscles have “first dibs” on the sugar in your bloodstream so they can move without having to worry about all your liver or fat cells pulling the glucose they need away from them.

How does this lead to a “sugar crash”? If you don’t move around when your BGLs go up, cortisol will eventually go away (it takes ~1.5-2 hrs, depending on activity & hydration) and insulin can start to do its job again. However, if your BGLs went up really fast and stayed up for a while, your pancreas (which releases insulin) will notice that the insulin currently in the blood is not doing its job and your BGLs aren’t coming down fast enough. So it thinks “I better turn this up to 11” and puts even more insulin into the blood. When the cortisol wears off, your cells will switch from not listening to the insulin’s message to paying attention to its every word. And the insulin is turned up to 11. So your cells pull as much glucose as they can out of the bloodstream. And your BGLs crash (~2-3 hrs after caffeine), making you feel sleepy (that 3 o’clock feeling is probably hypoglycemia.)

What would cause your BGLs to go up quickly and stay elevated? Two main culprits: (1) adding more glucose to your system when your body couldn’t respond to insulin and (2) not moving around so your muscles (which can pull glucose out of the bloodstream without insulin) couldn’t help lower your BGLs.

Staying hydrated and eating snacks high in fiber + protein helps keep your BGLs stable after caffeine. Staying hydrated makes sure that your system can clear the cortisol quickly. If you were moving around, your blood would pump and the cortisol would get filtered out. Plus, your muscles would bring your BGLs back into balance. If you aren’t moving, staying hydrated will increase your blood volume but not the total glucose in the blood (ie., the glucose will be less concentrated). Your pancreas and liver keep an eye on the glucose concentration and not the total amount, so stay hydrated.

Snacks high in protein and fiber will also help keep your BGLs from getting too high. This means that less insulin will be released, so you’re less likely to have too much insulin in your blood when your cells start responding to it again, and you’re less likely to have that over-reaction that causes hypoglycemia (low BGLs).

Metabolic tips to prevent that post-caffeine crash:

• Move around after drinking coffee; if you can’t, skip sweetening your coffee.

• Replace refined flour snacks with high fiber or protein snacks 30 min before and after to avoid an insulin spike that leads to a “sugar crash”.

• Drink a lot of water to help your system rebalance more smoothly.

*Some jobs demand that we don’t keep consistent schedules; they have also been associated with increased risk of Type 2 Diabetes and cardiovascular disease. This isn’t fatalistic - working the night shift doesn’t mean we will develop a metabolic disease, it means we’re more likely to. Being aware of your risk can help you take actions to balance it out.