Keto Side Effects: What to Expect and How to Fix Them
Common keto side effects like keto flu, constipation, and fatigue—plus exactly how to prevent and treat them with electrolytes and proper hydration.
The keto diet works for a lot of people—but it can come with side effects, especially in the beginning. Most of them are short-term and manageable. Some are more stubborn. A few are serious if ignored.
The good news? Almost all of these side effects can be prevented or minimized with the right approach. Here’s what you might feel, why it happens, and exactly what to do about it.
Common Keto Side Effects (Especially Early On)
1. Keto Flu
This is the most talked-about side effect—and for good reason. It feels like a mild flu.
Symptoms:
- Headache
- Fatigue
- Brain fog
- Nausea
- Dizziness
- Irritability
- Muscle cramps
What causes it?
Your body is switching from carbs to fat for fuel. That transition can throw off electrolytes and hydration.
How long it lasts:
Usually 2 to 7 days. Some people don’t feel it at all.
How to feel better:
The #1 solution is electrolytes. Here are the daily targets most keto experts recommend:
| Electrolyte | Daily Target | Food Sources | Supplement Option |
|---|---|---|---|
| Sodium | 3,000-5,000 mg | Salt, broth, pickles, olives | Table salt, bouillon cubes |
| Potassium | 3,000-4,000 mg | Avocado, spinach, salmon | Potassium citrate (check with doctor) |
| Magnesium | 300-500 mg | Dark chocolate, nuts, leafy greens | Magnesium glycinate or citrate |
Quick keto flu fix: Dissolve ½ teaspoon salt in a glass of water and drink it. This provides ~1,150 mg sodium. Many people feel better within 15-30 minutes.
Other tips:
- Drink 2-3 liters of water daily
- Have 1-2 cups of bone broth
- Don’t overdo exercise the first week—light walking is fine
Cleveland Clinic confirms electrolyte imbalance is a main cause of keto flu.
2. Constipation
Keto can slow things down if you’re not getting enough fiber or fluid.
Why it happens:
You cut out carbs like whole grains and fruit, which have fiber. Plus, dehydration is common on keto.
Fix it:
- Drink more water
- Eat low-carb, high-fiber foods (like chia seeds, avocado, leafy greens)
- Try magnesium citrate or a gentle stool softener if needed
3. Bad Breath
Some people get a metallic or fruity smell on their breath. That’s from acetone, a ketone your body makes during ketosis.
It’s harmless—but annoying.
What helps:
- Drink water often
- Use sugar-free mints or mouthwash
- It usually fades after a few weeks
Healthline explains this is a common sign you’re in ketosis.
4. Trouble Sleeping
Some people say they sleep poorly the first few weeks.
Why?
Your body is adjusting, and lower insulin levels can mess with sleep hormones.
Tips:
- Don’t eat right before bed
- Try magnesium before sleep
- Give it time—sleep often improves after the first month
5. Low Energy or Weakness (at First)
When your body runs low on carbs, you may feel drained.
This is temporary. Once you start using fat and ketones for fuel, most people feel more energetic.
Tips:
- Stay hydrated
- Eat enough calories
- Make sure you’re getting enough sodium, especially early on
Less Common (But Still Possible)
| Side Effect | Cause | What Helps |
|---|---|---|
| Muscle cramps | Electrolyte loss | Salt your food, try magnesium |
| Hair thinning | Rapid weight loss, stress | Eat enough protein and fat, be patient |
| Digestive issues | Too much fat, too fast | Ease into it, try digestive enzymes |
| Heart palpitations | Low magnesium or dehydration | Hydrate and check with a doctor if it continues |
Long-Term Concerns (If Keto Isn’t Balanced)
If you do keto wrong—eating only bacon and cheese—you might run into bigger issues.
Possible problems:
- Nutrient deficiencies
- High LDL cholesterol (in some people)
- Digestive trouble
- Loss of muscle (if protein is too low)
How to avoid them:
✅ Eat real food—lots of leafy greens, fish, eggs, nuts, healthy oils
✅ Don’t skimp on protein
✅ Track your bloodwork if staying on keto long-term
✅ Work with a doctor or nutritionist if you have health issues
Mayo Clinic says long-term risks include nutrient shortfalls and liver or kidney stress in some people.
Who Should Be Careful or Avoid Keto?
Keto isn’t for everyone.
Talk to your doctor first if you:
- Take insulin or diabetes meds
- Have kidney or liver issues
- Are pregnant or breastfeeding
- Have a history of eating disorders
- Are underweight or very active
Some people feel great on keto. Others don’t. It’s not one-size-fits-all.
How to Reduce Side Effects
Daily Electrolyte Protocol
Follow this protocol and you’ll avoid most keto side effects:
Morning:
- 8 oz water with ½ tsp salt and a squeeze of lemon
- Breakfast with avocado (high in potassium)
Midday:
- 1 cup bone broth OR another glass of salted water
- Lunch with leafy greens (spinach, kale)
Evening:
- 300-400 mg magnesium glycinate (taken with dinner or before bed)
- Continue drinking water throughout the day
Signs you need more electrolytes:
- Headache → usually sodium
- Muscle cramps → usually magnesium or potassium
- Heart palpitations → usually potassium or magnesium
- Fatigue → usually all three
Other Key Strategies
Stay hydrated: Aim for 2-3 liters of water daily. More if you exercise or live in a hot climate. Your urine should be light yellow, not dark.
Add electrolytes daily: The targets above are minimums. Active people or those who sweat a lot may need more.
Don’t under-eat: You still need adequate calories—especially in the first few weeks. Eating too few calories combined with low carbs makes side effects much worse.
Ease into it: Consider reducing carbs gradually over 1-2 weeks instead of going cold turkey. This can reduce the intensity of keto flu.
Eat real, nutrient-dense food: Focus on quality proteins, vegetables, and healthy fats. “Dirty keto” (just bacon and cheese) can lead to nutrient deficiencies over time.
When to See a Doctor
Most keto side effects are minor and temporary. But contact your doctor if you experience:
- Severe or persistent headaches
- Heart palpitations that don’t resolve with electrolytes
- Chest pain or shortness of breath
- Extreme fatigue that doesn’t improve after 2 weeks
- Significant hair loss
- Any symptoms that concern you
Summary
- Most keto side effects happen early and go away in a week or two.
- The keto flu is real—but you can reduce it with electrolytes and water.
- Long-term issues happen when the diet isn’t balanced.
- Not everyone should do keto. Check with your doctor if you have health conditions.
- The key to avoiding side effects: hydration, nutrients, and real food.