The ketogenic diet, or “keto” for short, is a popular eating plan. But what actually happens when you start this diet? The keto diet changes the usual way your body gets energy. Instead of using carbohydrates as the main fuel, your body starts to use fat. This shift happens through a process called ketosis. In ketosis, the liver breaks down fat into molecules called ketones, which become your body’s main energy source-including for your brain. In this guide, you’ll learn how the keto diet works, the main things to know if you try it, the possible health benefits and drawbacks, and answers to common questions.
What Is the Keto Diet and How Does It Work?
The keto diet is very low in carbohydrates and high in fat. It’s similar to other low-carb diets, such as Atkins, but is even stricter about carb limits. The main idea is to eat far fewer carbs and much more fat. This isn’t just about skipping bread or pasta. It changes how your body makes energy. With fewer carbs, your body has little glucose (the normal energy source from carbs), so it starts burning fat instead. Fat becomes your main energy source, both the fat you eat and any stored in your body.
The diet works because it puts your body in a special metabolic state. Cutting out carbs forces your body to use fat for fuel, and this is the key to how the keto diet helps some people meet their health and weight goals.
What Is Ketosis?
Ketosis is the state the keto diet aims to achieve. Usually, the body uses glucose from carbs for energy. When you eat very few carbs, glucose runs low. In response, the liver begins turning fat into ketones. These ketones replace glucose as the main source of energy for your body and brain.
This switch is like moving from a car that only runs on gasoline to one that also runs efficiently on another type of fuel. Entering ketosis means your body burns fat for energy. It’s important to remember ketosis is not the same as ketoacidosis. Ketosis is a normal, controlled process, while ketoacidosis is a serious medical emergency that mainly affects people with diabetes.
How Does the Body Enter Ketosis?
To get into ketosis, you need to greatly reduce carb intake-usually to about 20-50 grams of carbohydrates per day. For reference, a medium banana has roughly 27 grams of carbs. Instead of carbs, you eat more fat (like from meat, fish, eggs, nuts, and oils) and keep protein at moderate levels.
How long it takes to enter ketosis varies. Most people need two to four days, but for some it could take a week or more, especially if they’ve been eating lots of carbs. Your age, metabolism, exercise, and sleep habits can make a difference. Eating too much protein can slow things down, because extra protein can be turned into glucose. Some people add intermittent fasting to help speed up the process.
Keto Diet Macronutrient Breakdown
| Macronutrient | Standard Ketogenic Diet (% of daily calories) | Amount in 2,000 Calorie Diet |
|---|---|---|
| Fat | ~70% | ≈ 165g |
| Protein | ~20% | ≈ 75g |
| Carbohydrate | ~10% | ≈ 40g |
Some versions of keto add more protein (up to 35%) for different needs.
Keto Diet Guidelines and Rules
The keto diet is more than just a low-carb diet. It requires big changes to your usual meals. There are clear limits on carbs, a focus on healthy fats, and only moderate protein. Following these rules keeps you in ketosis, which is the main goal of the diet. Planning is key-reading nutrition labels and finding new recipes can help keep things interesting and make the plan easier to stick to.
How Many Carbs Are Allowed?
Staying in ketosis depends on keeping carbs low-between 20 and 50 grams a day. This is a much smaller amount than most people eat. For comparison, a cup of cooked white rice or two medium bananas could exceed your daily carb limit on keto.
What Foods Can You Eat on Keto?
- Meats: beef, pork, lamb, poultry, bacon, sausage
- Fatty fish: salmon, tuna, mackerel, trout
- Eggs: all types, especially whole eggs
- Dairy: butter, cream, cheese (cheddar, mozzarella, goat, blue, etc.)
- Nuts and seeds: almonds, walnuts, peanuts, chia, flax, pumpkin seeds
- Oils: olive oil, avocado oil, coconut oil
- Avocados
- Low-carb vegetables: spinach, kale, lettuce, broccoli, cauliflower, asparagus, bell peppers, celery, cucumbers, zucchini, mushrooms, onions, garlic
- Spices and herbs
What Foods Are Off-Limits?
- Sugar (soda, juice, candy, ice cream, cake)
- Grains and starches (bread, pasta, rice, cereal, crackers)
- Most fruit (except small portions of berries)
- Beans and legumes (lentils, peas, chickpeas, kidney beans)
- Root vegetables (potatoes, carrots, parsnips, sweet potatoes)
- Most processed foods, low-fat/“diet” foods
- Sauces high in sugar (ketchup, barbecue sauce, honey mustard)
- Unhealthy fats (processed or hydrogenated oils)
- Alcohol (beer, sweet wine, mixed drinks)
- Sugar-free snacks with certain artificial sweeteners
Possible Health Benefits of the Keto Diet
The keto diet was first used to help treat neurological diseases, but now it’s also looked at for its effects on weight and metabolism. Many people find it helps with fat loss and blood sugar control. However, results can differ, and more research is needed for some claims. If you have specific health issues, talk with a doctor before starting keto.
Does Keto Help With Weight Loss?
- The body burns stored fat when it’s in ketosis
- Many people lose weight faster than with low-fat diets
- High fat and protein help you feel full, reducing hunger naturally
- Studies found that low-carb eaters often lose more weight and fat
Keto and Type 2 Diabetes
- Carb reduction helps lower high blood sugar
- Losing weight can improve insulin use
- Some studies show big improvements in blood sugar control
- Less need for diabetes medicine in some people on keto
Other Possible Benefits
- May help heart health by improving cholesterol and lowering blood pressure
- Sometimes used to help treat certain types of cancer (ongoing research)
- Can reduce seizures in children with epilepsy
- Studied for possible effects on Alzheimer’s and Parkinson’s disease
- Might help with conditions like PCOS by lowering insulin levels
- May help healing after brain injuries (more research needed)
Potential Risks and Side Effects
While the diet has benefits, there are also possible downsides. Starting keto can make you feel uncomfortable for a few days, and long-term use may lead to other issues. If you have health conditions, it’s best to talk to a doctor before you start. Here are some common concerns:
What Is the Keto Flu?
When changing to keto, you can have flu-like symptoms. This is called “keto flu” and may last a few days to a week. Signs include tiredness, headaches, feeling foggy, dizziness, more hunger, sleep issues, and sometimes stomach troubles (constipation or diarrhea). Drinking enough water, getting enough salt and potassium, and eating until you feel full can help ease these symptoms.
Risk of Nutrient Shortages
Since keto cuts out some foods like grains, beans, and fruit, you might not get enough vitamins, minerals, or fiber. Problems can include lack of selenium, magnesium, phosphorus, or some B and C vitamins. Not eating enough fiber can also cause constipation. Planning meals carefully is important, and some people may need supplements to meet their needs.
Is Keto Safe for Everyone?
Keto isn’t safe for all. People with kidney disease, some liver problems, or certain rare metabolic issues should avoid it. Those taking medicine for diabetes also need to check with their doctor first. If you use medications such as SGLT2 inhibitors (for type 2 diabetes), keto can be dangerous. If you have a history of eating disorders, keto may not be a healthy option. Always talk to your doctor or a registered dietitian before starting this diet.
Common Questions About the Keto Diet
How Long Does It Take to Enter Ketosis?
For most people, cutting carbs to 20-50 grams per day leads to ketosis within 2-4 days. If you were eating lots of carbs before, it might take longer. Some enter in one day with fasting, others need a week. Individual factors like metabolism and activity level matter.
How Much Protein Is Allowed?
You should eat moderate protein on keto-about 20% of daily calories. Eating too much can raise blood sugar and slow ketosis. Most people should keep protein at or below 35% of their calories. For those who exercise a lot, especially with weights, a little more protein (about 1.5g per pound of body weight) is okay to help protect muscle.
Can I Occasionally Eat More Carbs?
When starting out, keep carbs very low. After 2-3 months, some people have small amounts of carbs for special events (like a slice of cake on a birthday), but this can slow or stop weight loss until you return to strict keto. Most people stick to the plan for better results.
Will I Lose Muscle on Keto?
Any weight loss diet can result in some muscle loss. Keto’s moderate protein and high ketones can help protect your muscle. Adding weight lifting or resistance exercises can minimize muscle loss, and may even help you build muscle.
Why Does My Breath Smell Bad?
When you’re in ketosis, your body makes more acetone, a type of ketone. This causes a strong, sometimes fruity smell on your breath, called “keto breath.” Drinking more water, chewing sugar-free gum, or using mints can help. This side effect usually lessens over time.
How Do I Deal With Digestive Problems?
Stomach problems (like constipation or diarrhea) often happen in the first few weeks. This is mostly because you are eating less fiber. Try eating more high-fiber, low-carb veggies (like spinach, avocado, chia seeds) and make sure you drink enough water. If issues continue, consult your doctor.
Is Ketosis the Same as Ketoacidosis?
No, they are very different. Ketosis (from keto diet or fasting) is a safe, normal process. Ketoacidosis is a dangerous, medical emergency, usually in people with type 1 diabetes who don’t have enough insulin. Ketoacidosis causes very high ketone and blood sugar levels and needs immediate medical treatment.
Main Points About How the Keto Diet Works
- The keto diet switches your body’s main energy source from carbs to fat by putting you in ketosis.
- Ketosis is reached by eating very few carbs, and more fat, with just enough protein.
- Following strict carb and food guidelines is key to seeing results and staying in ketosis.
- Possible benefits include weight loss, better blood sugar control, and improved risk factors for heart disease and certain brain disorders.
- Common side effects are temporary (such as “keto flu”) but long-term issues, like missing key nutrients, can happen if the diet isn’t well planned.
- The keto diet isn’t right for everyone. Always talk with a medical professional before making big diet changes, especially if you have health conditions.