It's not the first time you've heard a friend tell you they're "going keto," in the same casual tone that they might also tell you they're going to Trader Joe's or Target. But the mechanism of the diet itself is a lot less casual, and more intense than most people realize.

The ketogenic diet has an interesting evolution, with a medical history that dates back to the 1920s. The diet was originally designed as a way to treat epilepsy in children. It worked — or at least helped — and has since been adapted for use in other neurological disorders, sleep disorders, bipolar disorder, autism, and even brain cancer. It's favored among celebrities, Silicon Valley techies, and other social media influencers who tout the tasty fat-burning regimen, but it's also one of today's most Googled, top Pinterest performing diets that's likely flooding your Instagram feed, too.

Eat more beef, butter, and bacon, while losing weight and potentially boosting brain, mood, and sleep benefits, too? It's easy to see why some are so quick to sign the dotted line.

So, How Does It Work?

The diet is heavily weighted in fats; meals are based on meat, eggs, cheese, high-fat dairy (cream and butter), poultry, seafood, and plant-based fats like oil, nuts, seeds, and avocados. What's missing are most fruits, starchy vegetables (potatoes, carrots), whole grains, legumes, refined grains, sugar, and dairy.

At the surface it's another elimination diet; essentially a lower-carb version of a low-carb diet. Below that surface is where it gets a bit more interesting and complicated. The diet, when done rigorously and accurately, sends your body into a state of metabolic starvation. To back up just a bit, our bodies are fueled by carbohydrates, which are broken down into glucose. That glucose is then stored by the body — namely organs and muscle tissues — and used as its primary source of fuel. In the absence of available glucose, our bodies start breaking down fat for energy, into ketone bodies (a process called ketosis), to generate energy until carbohydrates are once again made available (if at all).

In a nutshell: The high-fat/low-carb combination aims to shift the body's metabolic focus away from burning carbs and sugar as fuel to burning fat, via ketones, produced by the liver. The ability to reach ketosis isn't instantaneous — it happens over several consecutive days of strict adherence to eating very few carbohydrates. How few? For most people it's between 20 and 50 grams a day. For reference, a banana has about 30 grams of carbohydrates, a 12-ounce IPA has about 20 grams, and a slice of delivery thin-crust pizza has about 25 grams. Numbers add up quickly.

So, What Do You Eat?

The ketogenic diet is rich in fat, moderate in protein, and includes plenty of meat, eggs, cheese, seafood, nuts and nut butters, plant-based oils, butter, seeds, and some vegetables (mostly non-starchy ones like zucchini, peppers, lettuce, cucumbers, cauliflower, and greens). Logistically speaking, it ends up being about 3 to 4 grams of fat for every 1 gram of protein or carbohydrate, or about 75 to 80% of your daily calories from fat.

So, why the hype?

Much like other lower-carb diets, such as Atkins and South Beach, weight loss success on the keto diet has proven to reap far more efficient and more effective results than traditional low-fat or Mediterranean-style diets. And like Paleo, sugar and gluten remain off limits; healthy fats like avocado, oil, and coconut are consumed in high quantity, and butter finds its way back onto the table (and even into coffee mugs!).

Read more: What's the Difference Between Keto, Paleo, and Atkins?

But unlike other low-carb diets, the keto diet doesn't ease up on its restrictive guidelines. To stay in ketosis, you must keep carbohydrate levels extremely low. The keto diet may be hyper-caloric, but the body burns fat, rather than glucose (also called glycogen), to feed cells. Plus, there's water weight loss. Each molecule of glycogen is attached to twice its weight in water. Extreme depletion of glycogen stores equals extreme water weight loss, which equals shedding of pounds. Such a tremendously high-fat diet keeps you fuller longer, so the desire to reach for that 3 p.m. bag of potato chips is far less likely on the keto diet. Ketosis suppresses the appetite; you're just not hungry.

Fewer grams of carbohydrates and sugar lead to fewer insulin surges, improved blood glucose levels, and better control of diabetic symptoms, according to a large portfolio of reputably published research.

And finally, when someone goes into ketosis, the brain uses ketones instead of glucose as fuel. There's a theory that these ketones might offer protective benefits to certain brain cells by being more energy efficient. With increased energy on reserve, the brain may be able to better defend itself from unwelcome disease-causing foreigners, and have the potential to directly inhibit neurological stress.

If you're considering trying keto, you should also consider the downsides: The diet is very extreme, very restrictive, and difficult to do correctly and safely maintain. Ketosis is a survival mechanism, and not exactly desirable long-term. In addition to being high-fat and low-carb, protein has very strict limits; too much of it will pull you out of ketosis and disrupt the metabolic process. Research on all prospective benefits is limited and inconclusive, so it's important to understand the potential risks before diving in. In the early stages, doers complain of "keto-flu" symptoms like headaches, dizziness, constipation, muscle cramping, bad breath, and loss of energy.

5 Things You Should Know Before Going Keto

1. Sustainability is questionable.

For people with brain disorders and diabetes, the keto diet can potentially offer health benefits and a way to manage and prevent certain symptoms. But studies are inconclusive and inconsistent. And for someone who just wants to lose weight, the long-term effects are currently unknown.

2. It's more of a lifestyle than a diet.

When you go into ketosis, you're actually shifting your body's metabolic format. These metabolic adaptations can make it difficult to "switch" back and forth to regular carbohydrate-based meals and snacks without gaining weight and upsetting metabolic balance. If you plan to go keto, you need to plan to go all in.

3. It's a harder diet to find a nutritional balance.

Without whole grains, legumes, fruit, and a number of vegetables, the keto diet is typically low in fiber and deplete of many vitamins and minerals found in these foods.

4. It eliminates added sugars.

Eliminating added sugars is something we all need to embrace. The same goes for adding more healthy fats (like avocado and olive oil) into our everyday meals.

5. It should be done under a doctor's supervision at first.

If you choose to attempt the keto diet, do so under a doctor's supervision, at least at first. Understanding where good fats come from (nuts, avocados, plant oils) and recognizing what foods contain carbohydrates is essential for proper adherence and success.

The Bottom Line

Chances are you're going to lose weight if you decide to go keto. And the brain-boosting, blood sugar-regulating benefits are well-supported, too. But ketosis is a state of metabolic stress; your body shifts into survival mode. It's important to ask yourself what the overall goal of going keto actually is. Going in and out of metabolic ketosis isn't good for you, nor are drastic ups and downs in your weight.

Balance, consistency, and moderation all play a role in optimal health, too — be cautious in how you approach anything with the word diet attached to it. The best diet is one that includes a lifestyle change that works best for you, your routine, and your health.

Please note: In no way am I endorsing nutritional ketosis as a best practice for sustained weight loss or supplement to medication.