Understanding the Risks and Side Effects of Keto

The keto diet a high-fat, very low-carb approach to eating has gained popularity for its fast-track weight loss benefits and potential blood sugar control. But while entering ketosis (a metabolic state where your body burns fat instead of glucose) can be effective for some, it may also come with side effects that range from uncomfortable to potentially serious.

If you’re considering keto, it’s essential to understand what it could mean for your health in the short and long term. Here are eight side effects to keep in mind before starting the keto diet.

1. Dehydration

One of the earliest and most common side effects of ketosis is dehydration. As your body shifts from using carbs to burning fat, it also excretes more sodium and water through urine. This rapid fluid loss can lead to:

• Headaches

• Dry mouth

• Dizziness

• Visual disturbances

How to manage it: Stay on top of your water intake and consider incorporating electrolyte-rich drinks or supplements early in your transition to keto.

2. Constipation

Carbohydrates are a major source of dietary fiber, so cutting them out can slow digestion and lead to constipation. This is especially common during the first few weeks on keto.

Signs of constipation include:

• Fewer than three bowel movements per week

• Hard or dry stools

• Pain or difficulty passing stool

What helps: Drink more fluids, and include high-fiber, low-carb vegetables like spinach, zucchini, and chia seeds. A fiber supplement may also be helpful.

3. Electrolyte Imbalances

Rapid changes in diet can throw off your body’s electrolyte balance, especially in the first few days of ketosis. This can lead to hyponatremia (low sodium) or hypomagnesemia (low magnesium).

Symptoms may include:

• Muscle cramps

• Fatigue or confusion

• Swelling (edema)

• Fast heart rate

• Shortness of breath

How to manage: Use electrolyte supplements as needed and make sure you're getting enough minerals through food or a multivitamin.

4. Keto Flu

The infamous “keto flu” isn’t a real flu but a cluster of symptoms that many people experience when first entering ketosis. It typically lasts a few days to a week.

Common symptoms:

• Headache

• Nausea

• Brain fog

• Muscle cramps

• Fatigue

• Digestive upset

How to feel better: Stay hydrated, rest, and consider easing into ketosis more slowly rather than making an abrupt shift.

5. Low Blood Sugar (Hypoglycemia)

Because the keto diet drastically reduces carb intake, blood sugar levels can dip, especially in people with diabetes or those taking insulin or other blood sugar-lowering medications.

Symptoms of hypoglycemia include:

• Feeling shaky or lightheaded

• Increased heart rate

• Irritability or confusion

• Hunger

• Headaches or blurred vision

Important: If you have diabetes or are on blood sugar medications, talk to your doctor before starting keto to avoid dangerous lows.

6. Nutrient Deficiencies

Strictly limiting carbohydrates often means eliminating a wide range of fruits, whole grains, and legumes foods rich in essential nutrients. This can lead to deficiencies in:

• B vitamins (thiamine, folate, B6, B12)

• Vitamins A, E, and K

• Magnesium and potassium

• Iron and calcium

• Linolenic acid (an essential omega-3 fat)

The risk: These deficiencies can lead to fatigue, poor immunity, cognitive issues, and bone loss.

What helps: A high-quality multivitamin and a dietitian-guided approach to keto can help prevent deficiencies.

7. Cardiovascular Risks

While keto often improves certain heart health markers like triglycerides and blood pressure in the short term, the long-term impact on cardiovascular health is unclear. Some studies link keto to increased levels of LDL (“bad”) cholesterol, which is associated with a higher risk of heart disease.

This may be due to:

• High intake of saturated fats

• Overreliance on animal-based proteins

• Low intake of heart-healthy carbs (like oats or beans)

Tip: If you choose to go keto, focus on plant-based fats (like avocado, olive oil, and nuts) rather than processed meats and butter.

8. Kidney Strain and Stones

High protein intake (common on many keto plans) and increased ketone production can raise the acidity of your urine, increasing the risk of kidney stones and over time, placing stress on kidney function.

Signs of kidney trouble:

• Sharp back pain

• Pain or burning while urinating

• Blood in the urine

• Cloudy or foul-smelling urine

If you have chronic kidney disease (CKD) or a family history of kidney issues, consult your healthcare provider before starting keto.

Is the Keto Diet Safe for Everyone?

While generally safe for many, the keto diet may be dangerous for people with certain health conditions, including:

• Liver failure

• Pancreatitis

• Type 1 diabetes

• Fat metabolism disorders

• Pyruvate kinase deficiency

• Pregnancy or breastfeeding

There’s also a difference between ketosis (a normal metabolic process) and ketoacidosis, which is a dangerous condition that typically affects people with unmanaged diabetes.

How to Approach Keto Safely

If you’re still interested in trying the keto diet, here’s how to get started more safely:

• Talk to your doctor or a registered dietitian first, especially if you take medications or have a medical condition.

• Ease into keto slowly, gradually reducing carbs rather than going cold turkey.

• Monitor your symptoms and consider testing for ketosis if advised by your healthcare provider.

• Choose nutrient-dense foods like non-starchy vegetables, healthy fats, and quality proteins.

Quick Stat Check:

• Up to 6.3 episodes of hypoglycemia per week were recorded in type 1 diabetics on keto in one study

• The body can lose significant sodium through urine in the first 2–6 days of ketosis

• Common nutrient deficiencies on keto include vitamin B12, magnesium, and potassium

The keto diet may be popular, but it's not risk-free. Before cutting carbs completely, weigh the benefits against the potential side effects especially if you’re managing chronic conditions or aiming for long-term health.

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