6 Things You Must Know Before You Try The Keto Diet

Remember the low-fat diet craze? Back in the 1990s, we were told that swapping regular cookies and chips for those labeled "low fat" would be the ticket to easy weight loss and better health.

Today, we know the push toward fat-free actually made us fatter — and the diet pendulum has swung in the other direction. Along with research that has shown weight loss is more effectively achieved through a high-fat, low-carb eating plan, health-conscious folks have fully embraced fat. Sales of whole-fat milk and yogurt have soared in recent years, and most nutritionists now tell their clients to incorporate fatty foods like fish, avocado, and olive oil into their diets. The reemergence of all this creamy goodness has led to a century-old diet making a major comeback: the ketogenic diet, or keto diet for short.

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What is the keto diet?

First, some context: the average person's diet contain about 55% carbohydrates, 30% fat, and 15% protein. On the keto diet, though, you eat a whole lot more fat, and a lot less carbs: 80% of the diet is comprised of fat, 15% is protein, and a mere 5% of calories come from carbohydrates. For someone on a 1,500-calorie diet, that translates to 19 grams of carbohydrates per day, which is less than what you find in one medium-sized apple.

Why the carb restriction? Well, your body's preferred fuel source is carbohydrates, so it will always turn to those first. If you eat fewer carbs, your body will burn through them faster, and will have to turn to start breaking down fat for energy. When this occurs, the body goes into a state of ketosis.

Is the keto diet effective for weight loss?

Does this really fuel weight loss or make us healthier? According to one Spanish study of 20 obese adults, the answer is yes. For the study, participants were put on a low-calorie keto diet and lost an average of 40 pounds over four months. Another small experiment had a similar outcome. In a six-month Experimental & Clinical Cardiology study of 83 obese adults, those on the keto diet lost an average of 33 pounds, while lowering their bad (LDL) cholesterol levels and increasing their good (HDL) cholesterol.

But all those studies were very small, and not all research on the keto diet is as promising. One American Society for Clinical Nutrition study of 20 participants found that those on the diet didn’t lose more weight than those on a non-keto diet. But they did have fouler moods and higher levels of inflammation, which has been linked to a variety of conditions, including heart disease and cancer.

What should you know before you try the keto diet?

Since research on the keto diet is fairly limited and inconclusive, it’s important to educate yourself about the potential risks before trying it.

Here, five things you should know before going keto:

1. Keto diet meal plans are pretty restrictive

Keto dieters eat mostly meat, healthy fats, and and non-starchy vegetables like leafy greens. And...that's pretty much it.

Here's a breakdown of keto-friendly foods, foods that are OK to eat occasionally, and foods keto eaters avoid.

Best keto foods

Fats: Olive oil, coconut oil, butter, avocado oil, MCT oil, avocados

Proteins: Beef, poultry, eggs, fish

Non-starchy veggies: Leafy greens, cruciferous veggies (broccoli, cabbage, cauliflower, Brussels sprouts), cucumbers

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Keto foods to eat sparingly

Full-fat dairy: Milk, cheese, yogurt

Medium-starchy veggies: Carrots, beets, parsnips, peas, artichokes, potatoes

Legumes: Beans, chickpeas, lentils, peanuts

Nuts and seeds: Almonds, cashews, walnuts, pumpkin seeds, sunflower seeds

Fruits: Berries, bananas, melons

Keto foods to avoid

All types of sugar: Including honey, agave, maple syrup

Grains: Wheat, oats, all types of rice, corn

All foods made with flour: Breads, pastas

Processed foods: Anything that comes in a bag or a box

Despite how limiting the ketogenic diet is, diet experts say that with careful planning, you can still fit in all of your vital vitamins and minerals. However, to play it safe, you should work with a nutritionist to come up with a well-rounded keto meal plan.

2. The long-term effects of the keto diet are unclear

Experts are split on whether the keto diet is a good idea. On the one hand, Lori Chang, registered dietitian and a supervisor at the Center for Healthy Living at Kaiser Permanente West Los Angeles, says using a “cleaner” source of energy — ketones rather than quick-burning carbohydrates — can improve mood and energy levels. When you eat refined carbohydrates or just too many carbs in general, the blood is flooded with excess insulin, Chang says. "This can lead to a blood sugar rollercoaster that stresses the body and negatively impacts energy levels and mood. When you’re in a state of ketosis, however, ketone bodies don’t require insulin to cross the blood-brain barrier, which wards off unfavourable blood sugar levels."

Other experts say the long-term accumulation of ketones could be harmful. “Those ketones are emergency fuel sources, and we’re not meant to run on them long-term,” says Kristen Kizer, a registered dietitian at Houston Methodist Hospital. “Ketones are negatively-charged molecules, which means they’re acidic. When you build up ketone bodies in your system, you’re building up acid. One of the ways your body buffers acid is by pulling calcium from your bones.” Kizer also notes that the diet isn't very balanced and involves a very high intake of animal products, which generally do not protect against cancer, diabetes, or other diseases.

If you do try the diet outside of medical supervision, Kizer says it’s important to test your urine with urinalysis ketone test strips (one to try: Ketostix Reagent Strips for Urinalysis) to ensure your ketone levels don’t become dangerously high. Ketone urine test strips are also used by people with diabetes to determine if they’re at risk for ketoacidosis (DKA), a life-threatening complication that occurs when an individual doesn’t have enough insulin in their body. (Healthy ketosis is considered 0.5 to 3.0 mM blood ketones.)

3. There's a thing called the "keto flu"—and it's not fun

Carbs hold fluids in your body (think of how bread soaks up water compared to a chicken breast), so when you cut back on the nutrient, extra water is excreted in your urine. This makes it vital for those on the keto diet to stay hydrated. Not only will drinking extra water ward off constipation, but it can also lower the odds you'll get the “keto flu,” a period of fatigue, headaches, and pain, often caused by dehydration and loss of electrolytes.

Other side effects of the diet may include an increased risk of kidney stones (due to dehydration and acidic urine that’s high in calcium), bad breath, muscle cramps, and dizziness. Further, depending on how you choose your fats, the keto diet can also contain an abundance of saturated fat, which raises levels of dangerous LDL cholesterol and causes atherosclerosis, the buildup of fats and cholesterol in the arteries. If you decide to go keto, have a doctor monitor your cholesterol levels monthly to ensure you remain within a healthy range.

4. The keto diet works really well for some people...

Heather Wharton, a 35-year-old business relationship manager from Tampa, Florida, lost 140 pounds since starting the keto diet in January 2016: “I plan on being on the keto diet for the rest of my life,” says Wharton. “My husband and I consider ourselves to be food addicts, and the keto diet is what we use as a form of abstinence from trigger foods that have sugar and other carbohydrates." (Here's how to tell if you have a food addiction.) A typical day of eating for Wharton includes coffee with a protein supplement, a cup of unsweetened cashew milk, cauliflower rice with ground turkey and liquid aminos (a carb-free substitute for soy sauce), spinach, six slices of turkey bacon, six eggs, and a little salsa.

Others consider the keto diet a short-term solution for weight loss. Tyler Drew, a 34-year-old real estate broker from Los Angeles, first read about the diet on Reddit and used it to lose 45 pounds in six months before returning to a traditional diet. While on the keto diet, Drew’s cholesterol levels improved, even though a typical day of eating involved bacon at both breakfast and dinner.

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5. ...But not so much for others

For some, ketosis can cause more negative than positive side effects. Dorena Rode, a 52-year-old author, and speaker from Occidental, California, tried the diet for a month and experienced heart palpitations and dizziness. Unlike Drew, Rode says her cholesterol increased from 192 to 250 mg/dL after she introduced more fat into her diet. (Less than 200 mg/dL is considered desirable, while anything over 240 mg/dL is considered high.)

6. Bottom line: Talk to your doctor to make sure the keto diet is safe for you

You’ve heard this line before, but really: Check with a doctor before trying the keto diet. The keto diet is an extreme eating regimen that could be harmful to certain people. It may not be right for those with heart disease, type 1 diabetes, or type 2 diabetes not controlled by insulin.

Although experts like Kizer have concerns about the keto diet, if you’re set on trying it, a doctor can help you determine if it is right for you and provide you with tools and information for accurately tracking your ketosis status.

If ultimately you decide that the keto diet isn’t for you, including a blend of healthy fats in your diet can still protect your brain, raise good (LDL) cholesterol, lower risk of heart disease, and help you stay satiated throughout the day.

This article originally appeared on Harper's BAZAAR UK.