The Ketogenic, Paleo, and Atkins diets are all low-carb, but they have important differences that could help determine which is right for you. Here's a rundown on the underlying philosophies, food dos and don'ts, and pros and cons of each.

Atkins

This granddaddy of popular low-carb diets began in the 1970s, and by 2004, when it was known as the "Steak and Eggs Diet," supposedly one out of 11 adults was on the diet. The allure — and the nickname — came from the idea that you could eat endless amounts of even the most indulgent foods (bacon galore!) and, as long as a carb didn't pass your lips, you'd still lose weight.

Atkins has evolved since then, but the premise is the same: All carbohydrates cause spikes in blood sugar levels, and those spikes cause us to store fat. In the "induction" phase of the diet, you severely restrict your carbs to just 20 grams. (To put that in context, the USDA recommends 300 grams per day for a 2000-calorie diet.) After induction, you slowly add more fiber- and nutrient-rich carbs back in — but only to a point. The big appeal is still eating as much fat and protein as you want.

Pros

• You won't be hungry!
• You'll feel satisfied: Eating fat and protein helps you feel more satisfied than munching on rice cakes, so at least for the short term, you don't feel deprived.
• Weight comes off quickly, although some of it will be water weight (see cons).
• The four phases allow you to slowly add some carbs back in, making it somewhat easier to sustain.
• Atkins has a line of snack bars, shakes, and frozen meals, which make compliance convenient (see cons).
• There is evidence that the diet helps improve both cholesterol and blood sugar levels.

Cons

• Your initial dramatic weight loss is a whole lot of water — you won't keep losing at the same level, and the minute you eat carbs again it will come back on.
• You can eat too much protein, which can cause serious liver issues. This can also prevent you from going into ketosis, which means you won't lose weight.
• Eating barely any carbs can, at first, make you feel cranky, lethargic, and even achy — not just because you miss your morning toast, but also because your brain takes time to adjust from processing glucose to ketones.
• Bad breath: Being in a state of ketosis causes stinky breath — and since the bad breath doesn't come from your mouth, brushing isn't going to help.
• The Atkins line of foods and snacks often contain artificial sweeteners and other processed ingredients.
• It is easy to pack in the unhealthy fats that gave this diet its bad rap. The onus is on you to pick healthy fats.
• You may wage an ongoing battle to get enough fiber, and constipation sucks.

Paleo

The idea is that our modern diet, which is full of refined foods and sugar, is at the root of many diseases, including cancer, diabetes, heart disease, and Alzheimer's. The solution? Eat like our hunter-gatherer ancestors did and eliminate all processed and "new world" foods, including dairy.

Unlike the Keto and Atkins diets, Paleo does not eliminate all carbohydrates: You can have sweet potatoes, winter squash, and more. But you can't have grains (wheat, rice, oats), legumes, sugar, or dairy. "We really consider the Paleo diet more low-glycemic than low-carb," says Dr. Amy Goss, who researches the healthfulness of diets at University of Alabama at Birmingham. "It is a basically healthful diet because it eliminates processed food, although I can't say there is a good metabolic reason to eliminate dairy."

Paleo is a simpler way of eating, and most of us will lose weight when we stop scarfing down cookies and chips. "Even if the scale doesn't budge, a low glycemic diet helps you lose abdominal fat, which is linked to metabolic disease (i.e., diabetes, hypertension, heart disease)," says Dr. Goss. And while you may weigh the same, when you lose fat and gain or keep lean muscle mass, she says, "You may look and feel different."

At its heart, the diet is more a lifestyle choice about nutrient-dense eating than it is a weight-loss diet. Not everyone will lose weight on a Paleo diet.

Pros

• The focus of Paleo is on whole, nutrient-dense foods. You eat protein, fruits and vegetables, and healthy fats (like those from avocado, nuts, and seeds).
• Low-glycemic diets have been shown to lower blood sugar and cholesterol and reduce visceral fat.
• You may lose harmful abdominal fat.
• You don't have to give up sweets, as long as they are natural (honey, maple syrup, etc.).
• You don't count carbs, calories, or anything else.
• Gut health: People with gut issues may find eliminating wheat, dairy, and processed foods also eliminates digestive discomfort.
• It is higher in fiber (and other nutrients) than Atkins and Keto.

Cons

• The diet is restrictive and difficult to implement.
• Be prepared to shop and cook for every meal, because it's challenging to eat out on Paleo.
• Reach deep into your pockets: Grass-fed meats, free-range poultry ,and organic produce get expensive.
• Without dairy, you may need to double down on your effort to consume enough calcium.
• Weight loss, if any, maybe be more gradual than on the other diets.

Keto

The goal of the keto (or, to be formal, ketogenic) diet is to get your body to burn fat for fuel. When it does, you are in "ketosis" — and usually drop significant weight. (Sound familiar? Atkins is based on the idea of going into ketosis.) The keto diet is high fat (60 to 75%), moderate protein (20 to 30%), and very low in carbs (around 5 to 10%, or 20 to 40 grams).

The diet, originally developed to treat epilepsy, has a whole lot of medical benefits in addition to weight loss. In her clinic, Dr. Goss says, "We know that at 20 grams of carbs a day, we'll get [patients] off their diabetes meds." When treating overweight patients, she says, they "always see improvements" in cholesterol numbers, and there is no need to restrict overall calories, she says, because "the dietary fat is so satiating, you just eat less."

Pros

• Satiety: The high-fat, high-protein foods make you feel more satisfied.
• You will really lose weight. Like Atkins, the initial loss is a lot of water weight, but keep going and there is a big payoff.
• You can eat up to four ounces of cheese. (For some of us, that's key.)
• Protein is more limited than on Atkins, so your liver will not end up processing it.
• Your cholesterol is going to get better: The good cholesterol will go up and the bad triglycerides go down.
• Your blood pressure will go down (see cons).
• The more you have to lose, the faster it will come off (see cons).
• The keto diet has been shown in some studies to improve the health of women with PCOS (Polycystic ovarian syndrome), reduce cholesterol, decrease seizures in epileptic children, and improve acne.

Cons

• The keto flu: As with Atkins, when you start the diet you may feel grumpy and foggy while your body and brain adjust to using ketones instead of glucose for fuel. (This can last from two days to two weeks).
• You cannot eat any fruit.
• Constipation. Again, the limited amount of fiber can cause issues.
• If you are on medication for hypertension, diabetes, or other conditions, you must talk to a doctor before starting the diet. For example, your blood pressure is likely to drop too far and you will need to adjust your medications.
• If you start with normal blood pressure, you may need to be careful that it doesn't go too low: Dr. Goss recommends her clinical participants drink broth (for the sodium) in the afternoon.
• You have to be careful about dehydration. You might need to take a sodium and potassium supplement.
• You'll want to get ketone urine testing strips to confirm you stay in ketosis.
• If you are accustomed to a high-fiber diet, you may need a supplement. (It varies by person.)