Paleo Flu: Symptoms, How Long It Lasts, What Helps

By Paleo Life Coach Editorial Team · Last updated September 25, 2026 · Nutrition from USDA FoodData Central

Day three of paleo, and instead of feeling amazing you have a headache, you’re tired by mid-afternoon and your legs feel heavy on the stairs. People call this the “paleo flu,” a borrowed name from the better-known “keto flu.” It isn’t an infection and it isn’t a medical diagnosis. It’s a loose cluster of symptoms some people notice when they change how they eat all at once.

This guide explains what’s likely behind it, how long it tends to last and what actually helps. It includes the sodium math most articles skip.

The quick version: “Paleo flu” describes headaches, tiredness, irritability, dizziness or cravings in the first days after starting paleo, usually when carbs and processed food drop sharply. Reports of the similar “keto flu” peak in week one and fade within about four weeks. Eating enough carbs, salting food, eating potassium-rich produce and drinking water usually help.

What is the paleo flu?

It’s an informal name, not a medical condition, and no study has examined it in paleo eaters specifically. The closest research is a 2020 analysis of 448 online forum posts about “keto flu” from people starting the much stricter ketogenic diet (Bostock et al., Frontiers in Nutrition). The most common symptoms reported were:

“Flu-like” feelings, headache and fatigue
Nausea, dizziness and “brain fog”
Stomach discomfort and lower energy
Feeling faint and heartbeat changes

Symptom reports peaked in the first week and dwindled after four weeks. Among the few users who reported when symptoms ended, resolution came between day 3 and day 30, with a median of 4.5 days. That’s forum data, not a clinical trial, so treat it as a rough picture rather than a prediction.

Paleo is usually far less extreme than keto, so many people notice nothing. Symptoms are more likely if your version of paleo also cuts carbohydrate sharply. The paleo carbs per day guide explains how to set a sensible carb range.

Why might you feel worse before you feel better?

Several ordinary changes can stack up in the first week:

Less carbohydrate. Swapping bread, pasta, cereal and sweets for meat and vegetables can halve carb intake overnight. Your body adjusts to burning more fat, and some people feel sluggish while it does.
Much less sodium. Processed food is the main source of salt in most diets, so cutting it cuts sodium dramatically (next section).
Fewer calories without meaning to. Vegetables and lean protein are filling but low in energy; eating too little makes anyone tired and irritable.
More fiber. A big jump in vegetables and fruit can cause gas or bloating at first. NIDDK suggests adding fiber gradually and drinking plenty of fluids (NIDDK).
Less sugar and fewer habit foods. Cravings are real, even if they aren’t a “detox.”

How much sodium do you lose when you go paleo?

Often more than 2,000 mg a day. The FDA reports that Americans eat about 3,400 mg of sodium a day on average, that over 70% comes from packaged and prepared foods, and that 2,300 mg equals about one teaspoon of salt.

A home-cooked paleo day is a different world. Here’s one computed from USDA data: eggs and spinach, a salmon and sweet potato bowl, chicken with roasted broccoli and cauliflower, walnuts and fruit, cooked with olive oil and no added salt.

How much sodium do you lose when you go paleo?
Scenario	Sodium per day
Average U.S. intake (FDA)	about 3,400 mg
Daily Value limit (FDA)	under 2,300 mg
Unsalted paleo day (USDA-computed)	about 550 mg
Same day + ¼ tsp salt (1.5 g)	about 1,130 mg
Same day + ½ tsp salt (3 g)	about 1,710 mg
Same day + ¼ tsp salt + 1 mug salted bone broth	about 2,060 mg

Paleo day calculated from USDA FoodData Central SR Legacy values (eggs, spinach, blueberries, salmon, sweet potato, kale, avocado, chicken breast, broccoli, cauliflower, walnuts, apple, olive oil). Table salt is 38,758 mg sodium per 100 g (FDC 173468); the broth is 1 cup home-prepared chicken stock (FDC 172884) with ¼ tsp salt, about 925 mg.

Going from about 3,400 mg to 550 mg overnight is a drop of nearly 2,900 mg. For most people with high blood pressure that’s a welcome change, and it’s one reason paleo trials often show lower blood pressure (see paleo vs DASH). But for an active person who sweats a lot, very low sodium can contribute to headaches, fatigue and cramps. Salting your food to taste, rather than fearing salt, keeps a whole-food paleo diet well under the 2,300 mg limit.

Are you getting enough potassium?

Probably more than before, which is good. The adequate intake is 2,600 mg a day for women and 3,400 mg for men, and average U.S. intake is below that (Harvard: potassium). The unsalted paleo day above supplies about 3,740 mg. Here’s where paleo potassium comes from:

Are you getting enough potassium?
Food (serving)	Potassium (mg)	Magnesium (mg)
Spinach, cooked, 1 cup	839	157
Sweet potato, baked, 150 g	713	41
Avocado, ½ (100 g)	485	29
Salmon, 4 oz cooked	434	34
Banana, 1 medium	422	32
Bone broth (homemade chicken stock), 1 cup	252	10

Calculated from USDA FoodData Central SR Legacy (FDC 168463, 168483, 171705, 175168, 173944, 172884).

You don’t need potassium pills for paleo flu; food is plenty. Potassium supplements can be dangerous for people with kidney disease or on certain blood pressure drugs, so don’t take them without medical advice.

What helps paleo flu? A practical checklist

Don’t cut carbs to zero. Include fruit, sweet potatoes, squash or plantains at most meals for the first two weeks. Paleo doesn’t require low-carb.
Salt your food. A quarter to half teaspoon a day across meals puts an otherwise unsalted paleo day in a sensible range. Iodized salt also covers iodine.
Sip salted broth. A mug of homemade broth with a pinch of salt is an easy electrolyte drink; see the paleo bone broth guide.
Eat enough. If you’re hungry and tired, add another portion of protein, fat or starch. The TDEE calculator gives a rough calorie target.
Drink water to thirst, more in heat or with exercise. Harvard’s water guide covers daily needs.
Ease into fiber. If you went from few vegetables to many, build up over a week or two.
Keep your usual coffee. Coffee is allowed on most versions of paleo (see is coffee paleo); quitting caffeine at the same time can pile on headaches.
Go easier on hard workouts for the first week or two.

For warming, salted, vegetable-heavy meals during week one, the paleo soup recipes are a good fit.

When is it not paleo flu? Talk to your doctor

Talk to your doctor before starting paleo, or right away if symptoms appear, in these situations:

You take diabetes medicines. Cutting carbs while on insulin or drugs that make the pancreas release insulin can cause low blood glucose. Signs include shakiness, hunger, dizziness, confusion and a fast or irregular heartbeat (NIDDK). Doses may need adjusting; see paleo diet for type 2 diabetes.
You take blood pressure medicines or diuretics. A big drop in sodium plus weight loss can lower blood pressure further. Diuretics are also a known cause of low blood sodium (MedlinePlus).
You have kidney, heart or liver disease, which affect how your body handles sodium, potassium and fluid.
You’re pregnant or breastfeeding.
Symptoms are severe or last longer than a few weeks, or you have confusion, fainting, chest pain, a racing or irregular heartbeat, vomiting or severe weakness. MedlinePlus lists confusion, headache, fatigue, muscle cramps and nausea among symptoms of low blood sodium, which needs medical evaluation (MedlinePlus).

Common paleo flu mistakes

“Pushing through” by eating even less. Hunger and fatigue usually mean you need more food, not less.
Avoiding salt on a whole-food diet. Once processed food is gone, a little salt at the table is usually fine; check with your doctor if you have high blood pressure or heart or kidney disease.
Chugging plain water to fix a headache. Very large amounts of water without food or sodium can make things worse.
Buying expensive electrolyte powders. Many contain sweeteners; broth, salted food and potassium-rich produce do the job.
Assuming every symptom is diet-related. A real flu, a new medication or dehydration can look similar.

Frequently asked questions about the paleo flu

What are paleo flu symptoms?

People describe headache, tiredness, irritability, brain fog, dizziness, cravings, low energy during exercise, muscle cramps and stomach changes in the first days or weeks after starting paleo. These overlap with the “keto flu” symptoms in a 2020 study of online forum reports. They aren’t caused by an infection, and fever is not part of it.

How long does the paleo flu last?

There’s no paleo-specific research. In the 2020 analysis of keto flu forum posts, symptom reports peaked in the first week and faded after about four weeks; users who reported recovery mentioned 3 to 30 days, with a median of 4.5 days. Because paleo is usually less restrictive, many people have milder or no symptoms.

Does everyone get the paleo flu?

No. Many people feel fine, especially if they keep eating fruit and starchy vegetables and salt their food. Symptoms are more common when people cut carbohydrates, processed foods, sugar and calories all at once, or combine the diet change with hard new workouts.

Should I take electrolytes on paleo?

Most people don’t need supplements. Salting food to taste, drinking salted broth and eating potassium-rich foods like spinach, sweet potatoes, avocado and bananas usually cover it. Ask your doctor first if you have high blood pressure, kidney or heart disease, or take diuretics or other blood pressure medicines.

What are the negative side effects of the paleo diet?

Short-term, some people get “paleo flu” symptoms, digestive changes from more fiber, or fatigue from eating too little. Longer-term risks come from what’s removed: calcium, vitamin D and iodine can run low without planning, and a version heavy in saturated fat can raise LDL cholesterol. Well-planned paleo avoids most of these.

Your next step: add carbs and salt back first

If you’re in the rough patch now, add a starchy vegetable or fruit to each meal, salt your food, have a mug of broth and eat until you’re satisfied for three days. Most people feel the difference quickly. For the longer-term gaps, read the paleo nutrient gaps guide, and check the common paleo mistakes list.

Consider this general nutrition reading, not a replacement for advice from your doctor, especially if you take medication for diabetes, blood pressure or heart or kidney conditions.

Paleo Flu: Why the First Weeks Can Feel Rough, How Long It Lasts and the Sodium Math Behind It