Every few years, a new diet emerges as the trendy answer to our everlasting nutritional woes. The grapefruit diet of the 1930s promised weight loss by eating the citrus at every meal. The Paleolithic diet says our genetics aren't meant for modern cuisine and excludes grains, beans, added sugars and even salt. Whole30 calls for the elimination of practically every food group over 30 days, then their gradual reincorporation in the sake of "reconnecting your relationship with food."

But perhaps none has been more popular — or controversial — than the ketogenic diet (or keto). Touted as a way to lose weight fast, manage diabetes and even treat epilepsy, keto works by restricting carbohydrate-rich foods such as grains, beans and fruits while increasing your intake of fat by anywhere from 70 to 90 percent of your diet.

The reality is, as much as keto may benefit certain conditions, following such a strict diet is not without risk, says Amanda Beaver, a registered dietician at Houston Methodist.

"There are different ways to go about following a keto diet that play a big role in how bad or good it is," says Beaver. "We know that healthy fats found in nuts, seeds and oils like extra virgin olive oil can be very beneficial for our heart health. However, keto also has the potential to be very bad for our heart health if individuals are choosing foods like bacon, sausage, butter and lots of red meat."

There are lots of ways to approach keto, some riskier than others. Whether you're already on keto or simply keto-curious, this article explores keto in detail, including how it works, the benefits, risks and important considerations based on your health goals.

What is the keto diet and how does it work?

At its simplest, the keto diet is a pattern of eating that limits carbohydrates while substantially increasing fats so that your body enters ketosis, a state when the body burns fat for energy instead of carbs. It's similar to the popular Atkins diet, another low-carb, high-fat diet, but takes the philosophy to the extreme by prescribing even less carbs and even more fat.

Under normal circumstances, the body's main energy source comes from breaking down carbohydrates into simple sugars called glucose. In ketosis, however, the body uses up its supply of glucose (called glycogen in its stored form), and is forced to use fat as the most available energy source. Fat breaks down into substances called ketones, acids typically used as backup power during times of fasting or long exercise. With keto, they're the main energy source.

How many carbs can you eat on keto?

Not many. According to keto guidelines, less than 10 percent of your diet should be carbohydrates, 10 percent to 20 percent should be protein and the rest — 70 percent to 90 percent — should come from fat. But Beaver emphasizes that your specific ratio will depend on your health goals. Epilepsy patients, for example, need to be on the higher end of the spectrum for fat and the lower end for protein and carbs for keto to be therapeutic, she notes.

What are the potential benefits of keto?

Weight loss

Keto is one of the most popular diets for weight loss. But it's not exactly fat being lost at first; it's mostly water weight.

Sugar naturally attracts water — it's why brownies and cakes stay moist after baking. Glycogen, the body's sugar stash, also holds onto water, but without carbs to replenish it, that extra water is no longer needed and is flushed out. It's why keto has such fast weight lost at first, but it doesn't last.

"Early on with keto, your weight loss will outpace other diets," Beaver says. "But when we look at a year out, research shows it's not necessarily more effective than other types of diets."

Lower cholesterol

We need fats to survive, but too much saturated fat can increase your risk of heart disease. Keto, Beaver says, has the potential to raise good cholesterol (HDL), and could even lower bad cholesterol (LDL), but you have to "really focus on eating lots of healthy fats and fiber." Otherwise, she says, keto tends to raise both HDL and LDL.

Treatment of epilepsy

For some, keto isn't just a popular diet — it's their treatment plan. While dietitians want people to be on the least restrictive diet possible, Beaver says, therapeutic diets can be very helpful for certain conditions. Keto is one of those diets that stand to benefit certain conditions, such as epilepsy, and has since the early 1920s.

Lower A1C

Many diabetic patients turn to keto to lower their A1C, a measurement of your average blood glucose over the last three months. Since glucose comes from carbs, the idea is that if you remove carbs from the equation, it will improve a patient's diabetes. However, Beaver says keto isn't the only diet or lifestyle choice that can achieve a lower A1C.

"Yes, diets lower in carbohydrates and carbohydrate counting can be very effective at lowering A1C," says Beaver. "But for people wanting to lose weight or those with diabetes, there are much less restrictive diets out there that can accomplish weight loss and lower A1C."

In fact, the American Diabetes Association created the "Diabetes Plate," a visual method to properly proportion servings so meals are healthy and manage blood sugar. Carbs make up a quarter of the plate.

Furthermore, Beaver says keto can actually be dangerous if patients also take certain medications that lower their blood sugar. So it's important people with diabetes talk to their doctor before starting keto or making any dietary changes.

Finally, although not diet-related, Beaver says exercise also has the power to improve insulin sensitivity. The effects of just one workout can last for hours — sometimes even a day or two.

What are the potential risks of keto?

Not sustainable

"A big reason many health professionals don't recommend keto is that it's not a sustainable diet," Beaver says. "The weight loss that happens at the beginning of keto is exciting, but after stopping, research shows that most people will return to their previous weight and may even gain more back."

Beaver says lots of people end up stopping keto because it's just so hard to maintain and live a normal life. Celebrations like birthdays and dinners quickly become troublesome tasks to keep keto. Typically, you end up having to eat lots of meat and cheese, which are high in saturated fats.

Disordered relationship with food

Weight loss, Beaver says, is not meant to be rapid or quick. In fact, the expectation of quick weight loss from dieting can not only impact our long-term health and metabolism, but it can also alter our perception of food for the worse, she says.

"Rapid weight loss is where you can get into some troublesome territory," says Beaver. "A lot of people want to lose weight for a big event or a wedding, and it's valid to want to feel your best for those things, but at the same time, extremely fast weight loss isn't good for you."

"With keto and other fad diets, people can sometimes develop a disordered relationship with food and carbohydrates in particular, where people feel all carbs are bad," she adds. "This 'all or nothing' mentality of dieting has the potential to wreck our relationship with food and can set people up for lots of weight cycling."

Weight cycling, or yo-yo dieting, is the repeated loss and gain of weight, often due to short-term bouts of restrictive eating patterns — and this "all or nothing" mentality is prevalent across many fad diets, not just keto:

• Whole30 involves eliminating and re-incorporating almost every food group
• The Paleo diet restricts all grains, beans, added sugars and salt
• The carnivore diet is all meat and dairy — no veggies allowed
• Juice cleanses promise "detoxification" by restricting all solid foods

Ultimately, "quick weight loss is not effective," says Beaver. You're less likely to keep it off and maintain it, but you may also risk losing muscle mass important for metabolism and even suppress your immunity.

(Related: 4 Fad Diet Red Flags to Watch Out For)

Increased bad cholesterol

It's tempting to consume lots of cheese, butter and red meat when keto is already so restrictive, but all of these foods are high in saturated fats, which can raise bad cholesterol.

"Before starting keto, I would recommend getting your cholesterol checked with your doctor as a baseline, then after you've been on the diet for a while, have it rechecked and see how your numbers are affected," Beaver says. "I've worked with patients who after keto, saw their LDL, or bad cholesterol, spike, even in people who didn't have high LDL to begin with."

Nutritional deficiencies

"Because carbohydrates are so limited on keto, the diet excludes lots of really nutritious foods that we know from studies are so beneficial to our health," says Beaver. "Fruits, whole grains and most starchy vegetables like beans and lentils are all very beneficial to our heart health that, for the most part, are excluded from keto."

"People potentially miss out on lots of fiber and can be at risk for deficiency in certain vitamins like magnesium, potassium and folate," Beaver adds. "People on keto need to thoughtfully include veggies, berries, and nuts to ensure they do not become deficient."

Magnesium, potassium and folate are examples of essential nutrients, meaning that the body cannot make them, that they must come from outside sources, like diet and supplements. A deficiency in any of these nutrients has the potential to cause health problems.

(Related: Are You Getting Enough Vitamins in Your Diet?)

Diabetic ketoacidosis

As Beaver mentions, keto can be dangerous for diabetic patients, especially if they take any medications that lower blood sugar, as it can not only cause a dangerous drop in blood sugar and inadvertently trigger diabetic ketoacidosis — a life-threatening condition in which the body makes too many ketones too fast. Always consult your doctor about any dietary changes, especially if you are diabetic.

Is there a healthy way to eat more fat?

"Absolutely!" Beaver exclaims. "There are so many highly nutritious fats we can include in our diet like seeds such as flax, chia, pumpkin and hemp; nuts such as walnuts, almonds and nut butters; and oils rich in monounsaturated fats such as olive oil and avocado oil."

The Mediterranean Diet, the second most heart-healthy diet according to the American Heart Association, surprisingly comprises up to 40% fat, which is "a lot of fat" says Beaver, but most of it comes from those "really nutritious" fats from nuts, seeds and plant oils.

Unsaturated fats are generally considered "good" fats and are known to lower your cholesterol. Saturated fats found in meats and dairy are mostly considered "bad" fats because they can raise your bad cholesterol, which is one reason they should be eaten in moderation. According to Beaver, most dietitians recommend including one fat (preferably a good fat) at each meal to enhance its filling power and boost our good cholesterol.

Is there a healthy way to consume carbs?

"Carbohydrates get a bad rap because people tend to lump all carbs into the same category," Beaver says. "Both black beans and donuts are high in carbohydrates, but they are not the same!"

Beaver says nutrient-rich, complex carbohydrates have the power to "greatly improve our health" when eaten regularly. Those include foods like:

• Potatoes and sweet potatoes
• Peas
• Whole grains
• Oats
• Beans
• Hummus
• Lentils
• Fruits
• Corn

"In contrast, refined grains, or processed carbs, especially when eaten in excess, are responsible for the detrimental effects many people associate carbs with," Beaver says. Those foods include:

• Sweetened yogurts
• Soda
• Candy
• Baked goods
• Fruit juices
• Some breakfast cereals

(Related: Are Simple Carbs Always Bad? Are Complex Carbs Always Better?)

If you've tried keto or are considering it

While keto has a place in improving conditions such as epilepsy, the truth is for long-term health, weight and diabetes management, Beaver emphasizes that there's no silver bullet out there and that fad diets like keto offer just a temporary solution for the long-term journey toward better nutrition and health. In other words, it's a marathon — not a sprint.

"Take a hard look at your history of dieting before starting keto," Beaver says. "If following past diets resulted in repeated weight loss and gains, consider seeking a more sustainable approach, including diet changes that actually work for you, balanced meals that focus on nutritious eating and more movement in your day."

"These habits are easier to maintain and, if continued, have the power to make lasting benefits on your health," she adds.