Why do you get tired after meals? Read on to learn more about post-meal fatigue and how you can help combat that middle-of-the-day tired spell or the crushing post-dinner feeling of tiredness.

Fatigue Is (Mainly) from the Hypothalamus

All of the most important reasons for fatigue have to do with the hypothalamus, which is something I discuss quite a bit.

Several hypothalamic areas, such as the suprachiasmatic nucleus (SCN), lateral hypothalamus (LH), and ventromedial hypothalamic nucleus (VMH) are implicated in the regulation of sleep, wakefulness, and food intake [R].

NOTE: In the scientific literature, post-meal fatigue is known as “post-prandial fatigue.

Post-Meal Fatigue Is a Metabolic Problem

Metabolism is the process where the energy goes in (caloric intake) and that energy is utilized by the body.

When energy isn’t utilized the way it’s supposed to, you have a metabolic problem.

For example, if you’re obese, the calories you take in are not being expended by having more physical and mental energy. Instead, it’s being stored as fat. That’s a metabolic problem.

Another metabolic problem is when you expend more calories than you take in and you get too thin. These calories might not be digested – they may be used for your immune system to create inflammation, or you might have increased body temperature.

Being too thin or too overweight are both metabolic problems, just of a slightly different nature.

When you take calories in, they are supposed to be used by your cells and make you feel more energetic, think more clearly, and have a better mood.

13 Reasons You Get Tired After Meals

1) Carbs and Glucose (by Suppressing Orexin)

I’ve written about orexin extensively and I’ve also written a post on fatigue after meals (has all the references).

It’s well known that too much glucose in the blood suppresses orexin, which is the most significant peptide that controls wakefulness. It’s most active in the hypothalamus.

Any carb will end up breaking down into glucose, so if you eat too many carbohydrates, you feel tired after a meal.

When I eat too many carbs or too much glucose, I get tired. This used to be the case much more than it is now.

The reason why glucose used to affect me has more to do with changes in the hypothalamus. I’ve noticed that lectins (by causing inflammation) make me more sensitive to glucose-induced fatigue. Since I restrict dietary lectins and other plant immunostimulants, this problem minimized.

In general, carbohydrates and plant-based foods contain a diverse range of chemicals that are capable of spiking your immune system (i.e., causing inflammation), if you’re susceptible.

2) Inflammation (by Suppressing Orexin)

Inflammatory cytokines like TNF and IL-1b can suppress orexin.

Many people have undiscovered food sensitivities and get inflammation from some component of their meals.

This was the most significant cause of fatigue after meals for me, and when I took out all of the foods that caused me inflammation, the post-meal fatigue went away.

If you are struggling with post-meal fatigue, you may want to try out the Lectin Avoidance Diet to figure out the food items that cause your fatigue due to inflammation.

3) Acidity, Orexin, and Post-Meal Fatigue

Orexin is extremely sensitive to the minor changes of pH in the blood.

When blood acidity temporarily goes down and your blood becomes slightly more alkaline, orexin is more likely to be suppressed and tiredness will ensue.

When you chew, your stomach needs to create hydrochloric acid (HCL), which is very acidic. This pulls some acidity out of your blood and temporarily causes a small increase in pH (lower acidity).

See my post on orexin for sources.

4) ATP and Orexin

Orexin is suppressed by glucose, as mentioned. But, when we have enough filled energy-related molecules including adenosine triphosphate (ATP) and pyruvate, orexin isn’t as easily suppressed [R].

Indeed, researchers have found that in CFS, people have less pyruvate in their cells.

Mitochondria are what control the production of energy-related molecules.

This means that if your mitochondria aren’t working well and you’re not producing adequate ATP, a meal with carbs is more likely to make you tired.

Digestion is an energy-intense process and I wouldn’t be surprised if it used a lot of ATP. Also, if you are getting inflammation from the food, that will deplete your energy reserves even more.

5) Leptin and Post-Meal Fatigue

When you eat, leptin goes up.

Leptin is capable of spiking inflammation and making you tired. Leptin spikes are associated with fatigue in studies.

Interestingly, leptin increases more from carbohydrates than protein or fat, which may explain, in part, why carbs make people more tired than other macronutrients.

When you have an inflammatory environment, leptin is capable of causing much more inflammation, which is why fatigue only occurs from leptin if you already have inflammation.

Indeed, this is one reason why carbs make people feel more tired.

6) Low NAD+/SIRT1 and Post-Meal Fatigue

NAD+ is important for DNA repair, stress resistance, and cell death [R, R].

NAD+ also increases metabolism and acts as a signal for energy balance. When your mitochondria are working well, you produce more NAD+, and this sets in motion a bunch of signals to increase energy intake and expenditure.

NAD+ makes you more insulin and leptin sensitive. When you have low levels, your general energy declines, your mitochondria works poorly, you have higher blood sugar, and this increases the risk of post-meal fatigue.

7) Less Blood Flow to the Brain

When you eat, the blood vessels of the GI tract dilate, increasing local blood flow. Blood rushes to your stomach to start processing the food.

Since the blood is moving to your GI system, this means your brain has less blood and therefore less oxygen and nutrients. This can contribute to fatigue.

8) Parasympathetic Activation (Rest and Digest)

When you eat, your parasympathetic system (rest and digest) increases, and the sympathetic system (fight or flight) decreases. This happens regardless of the composition of the meal.

Think about how you feel relaxed after a bowel movement. That’s parasympathetic activation.

I experience this a bit after a meal, but it’s more of a relaxation than a fatigue – and to the extent that I do feel tired, it’s very mild and dissipates quickly.

Regardless, parasympathetic activation can contribute to post-meal fatigue.

9) Circadian Rhythms and Fatigue

Daily-Rhythm-Sleep-Wake-Cycle

You might notice that you feel more tired after lunch than breakfast or dinner.

This is because there’s a rhythm to wakefulness and at around 1 to 3 PM, you naturally feel more tired. This is called the afternoon dip.

After 10 AM, sleep urge starts to go up, peaking around 2 PM. The wavy orange/red line shows the circadian rhythm of fatigue. The other part (sleep need) illustrates the steady buildup of metabolic products such as adenosine that cause fatigue.

The bottom line is that you are more likely to get tired after lunch for circadian reasons.

10) CCK and Post-Meal Fatigue

Cholecystokinin (CCK) is a significant factor in post-meal fatigue.

CCK is a gut hormone that’s mainly released in response to a fat-rich or lectin-rich meal. Long chain fats (saturated, MUFAs, PUFAs) are especially potent CCK inducers [R].

A high protein diet also increases CCK.

Studies will often use the fat from olive oil to induce CCK to release (oleate), which I’ve noticed pretty potently releases CCK for me [R].

CCK is responsible for:

  • Causing sleepiness/fatigue because it directly interacts with the hypothalamus (despite the fact that it activates orexin [R]
  • Inhibiting hypothalamic noradrenaline, which is a plausible mechanism for CCK’s fatigue-inducing and appetite-suppressing effect [R]
  • Stimulating wakefulness and fatigue in the hypothalamus

Giving a CCK blocker to rats prevented post-meal fatigue, whereas in humans it actually increased post-meal fatigue [R].

It’s accepted that CCK has sleep-promoting and wake-promoting properties, but the balance depends on other factors, in my opinion. If your hypothalamus is working well, it may be more wakeful promoting and if not, it can be more sleep-promoting.

CCK also:

  • Directly interacts with the hypothalamus to stimulate the flow of your colon, which will cause gas [R]
  • Follows a circadian rhythm and is likely released more in the daytime when our system is primed to eat
  • Increases bloating
  • Decreases stomach acid
  • Causes gut pain hypersensitivity [R]
  • Causes nausea, anxiety, and satiation

People with IBS are more likely to release too much CCK (a gut hormone) in response to a fat-rich meal.

In rats, legume lectins (and probably others) cause increased secretion of CCK. [R].

CCK receptors are made of sugars that are the target of lectins, such as wheat germ agglutinin [R].

11) Insulin, BCAAs, and Tryptophan

When you eat, insulin goes up. Insulin stimulates the uptake of valine, leucine, and isoleucine into muscle, but not tryptophan.

The theory is that this lowers the ratio of these BCAAs in the bloodstream relative to tryptophan.

Uptake of tryptophan by the brain thus increases. In the brain, tryptophan is converted to serotonin, which is then converted to melatonin. Increased brain serotonin and melatonin levels result in sleepiness.

This might be why eating a higher protein meal can blunt the fatigue a bit.

However, I do believe that this may be more significant for some people. For example, in people with CFS, serotonin increases more in response to a tryptophan load [R].

When I take things that increase serotonin (such as 5-HTP), I do get tired, so it makes sense that this explanation is more pronounced if you’ve got the genetic predisposition.

12) Insulin-Induced Low Potassium

Insulin causes serum potassium outside of the cells to go inside.

This can lead to a lower potassium state. The effects of low potassium include fatigue, muscle weakness, or paralysis.

However, when I supplement with potassium, it has a very small effect. This is certainly not very significant for me.

13) Cannabinoids and Orexin

Cannabis is more often associated with making you sleepier, but in actuality, low levels of cannabinoids potentiate orexin and can stimulate wakefulness.

I’ve noticed that post-meal fatigue is more common when people have variations in their cannabinoid receptors. That could have to do with cannabinoids activating orexin, or it could have to do with people with these variations being more sensitive to foods and therefore they have more inflammation from their diet.

Top Ways to Prevent Post-Meal Fatigue

Some of the most significant changes that have helped get rid of my post-meal fatigue were reducing plant-based foods in my diet (grains, beans, nuts, and seeds), consuming fewer carbs, and increasing my protein intake. See the lectin avoidance diet.

I have a more comprehensive anti-fatigue solution in the SelfHacked book.

With SelfDecode, people can get a closer look at their genetics, which can help home in on the root cause of their fatigue.

Here are some of the best methods to help post-meal fatigue. These recommendations are a product of an insane amount of research and experimentation.

  1. Eat more protein with meals.
  2. Avoid lectins.
  3. Reduce carbs (to reduce leptin and insulin spikes).
  4. Get sun on most of your body. Sun improves metabolism, mitochondrial function, and blood flow. It also stimulates the dopamine system, which helps with wakefulness.
  5. Use an ICES device on your head and gut. ICES increases oxygen utilization.
  6. Drink apple cider vinegar with meals to increase metabolism, acidity, and NAD+, and to lower blood sugar.
  7. Drink kombucha with meals (for lactate, to prevent orexin suppression).
  8. Take fish oil/DHA to reduce inflammation and improve mitochondrial function.
  9. Nicotine increases metabolism, NAD+, and orexin.
  10. Forskolin (95%) increases mitochondrial function.
  11. An infrared sauna activates the nervous system.
  12. Take inositol before a meal to reduce inflammation and insulin resistance.
  13. Take curcumin a half-hour before a meal to reduce inflammation.
  14. Use butyrate a half-hour before a meal ( you will notice the benefits the day after).
  15. Have black cumin seed oil with a meal to reduce inflammation.
  16. Andrographis reduces inflammation.
  17. Caprylic acid increases energy production (ketones).
  18. Add more potassium to your diet.

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