Unlimited butter. All the avocado. Bacon in bulk. Sound like a dream diet? A lot of people agree with you, which is why the ketogenic diet (keto for short) is having a serious moment right now. In fact, it's among the top three diets Millennials want to try in 2019, according to .
But there's more to this diet than just eating foods that were once viewed as off-limits. The high-fat, moderate-protein, low-carb diet is basically on the opposite end of the spectrum as your mom's 1980s low-fat regime — but how does it work? We turned to a handful of nutrition experts to find out.
What is the keto diet?
"The keto diet is a high-fat, moderate-protein, and very low-carb way of eating that leads to ketosis, which is a metabolic process that shifts the body to utilize a different power source," says , MS, RD, a registered dietitian at who specializes in sports nutrition, weight loss, and diet trends. It's similar to the Atkins diet, but is even lower in protein and higher in fat. In short: "Your body turns fat into fuel instead of running on easy-to-access carbs, which are its energy fuel source," says Nisevich Bede.
The keto diet dates back to the 1920s, explains Michelle Hyman, MS, RD, CDN a registered dietitian at . "The original keto diet was designed for patients with forms of epilepsy that were resistant to standard treatments. The macronutrient breakdown was designed to mimic the fasting state — which seemed to help with relieving seizures — yet provide energy and nutritions to function," Hyman says.
The Mayo Clinic promoted the menu as four parts fat to every one part carbohydrate and protein combined (4:1 ratio), for a diet that added up to 90% of calories from fat, 5% from protein, and 5% from carbohydrates.
Today, a few different variations exist, but the strict keto diet calls for 70 to 80% of calories from fat, 10 to 20% from protein, and 5 to 10% from carbs. The goal is to restrict carb consumption to between 20 to 50 grams of carbs per day to trigger ketosis.
The typical American consumes about 52% of calories from carbs, 33% from fat, and 16% from protein, according to a study published in . This macronutrient breakdown is fairly close to current dietary recommendations from the United States Department of Agriculture, which recommend 55 to 60% complex carbs, 30 percent fat and 15% protein to help prevent cardiovascular disease.
What is ketosis and how do I know when I'm experiencing it?
"Ketosis occurs when ketones are present in the body," Nisevich Bede says. "Ketones are normally present in small amounts during times of fasting, like right after you wake up. But when you're effectively following the keto diet, ketone levels are higher."
Technically speaking, you're in ketosis when your blood ketones are higher than 0.5 mmol/L, but the optimal level for fat-burning purposes is 1.5 to 3 mmol/L. Nisevich Bede says that seasoned keto dieters report that they can actually feel a difference in this state, citing that they're less hungry and experience mental clarity once they reach ketosis.
You may be able to tell that you're in ketosis by a change in your breath (many report halitosis, or bad breath, due to higher levels of the ketone acetone coursing through the body). Others experience the keto flu for anywhere from one day to two weeks as the body cranks up the ketones. Symptoms of the keto flu are very similar to the influenza virus, including nausea, fatigue, vomiting and diarrhea. Hydrating well and starting slowly can reduce your risk for this.
To see where you stand on the ketosis scale, you can test your ketone levels with a or with , the latter of which works similar to a pregnancy test and generally costs less than a dime a piece. Recent research shared in , however, found that (typically $200 to $300) provide the most accurate readings. Dozens of meters of all three formats are currently available on Amazon.
What are the health benefits of the keto diet?
"So many people are intrigued by the keto diet because it promises rapid weight loss. When weight loss occurs quickly early on, individuals are often more motivated to stay the course," Hyman says. "This is especially the case for those who have tried many diet plans before with limited success."
Initial research has found that the diet can help maintain — even as they shed pounds — and may also lead to increased appetite suppression. "A keto diet is an option for people looking to lose overall weight, lower fat mass, and even build muscle. As a dietitian who focuses on sports nutrition and weight loss, I also recommend it for my clients who need a strong break from their sugar cravings, as it lessens blood sugar spikes and the cravings that can accompany high sugar intake," Nisevich Bede says.
In addition to those in need of a sugar roller coaster reset, individuals with these conditions may particularly benefit from trying the keto diet, Hyman says:
- Polycystic Ovary Syndrome (PCOS)
- Alzheimer's disease
- Certain types of cancers
- Parkinson's disease
- Amyotrophic Lateral Sclerosis (ALS)
If you're considering a keto regimen, consult with your doctor and/or dietitian before doing so, and have regular blood tests along the way to make sure cholesterol and other levels stay within healthy ranges.
"It's important to still think about your protein intake to help avoid muscle loss, too," Nisevich Bede says.
What can I eat on the keto diet?
Here's a breakdown of the percentage of each food group you should be consuming every day, as well as what kinds of foods are best to consume for this diet.
Carbs (5-10% of calories): Tomatoes, eggplant, asparagus, broccoli, cauliflower, leafy greens, cucumber, bell peppers, zucchini, celery, Brussels sprout
Protein (10-20% of calories): Chicken (dark meat if possible), turkey (dark meat if possible), venison, beef, fish and seafood (especially fatty fish like salmon, sardines, tuna, and mackerel), pork, lamb, eggs, natural cheeses, unsweetened, whole milk plain Greek yogurt, whole milk ricotta cheese, whole milk cottage cheese
Fat (70-80% of calories): Olive oil, avocado oil, olives, avocados, flaxseeds, chia seeds, pumpkin seeds, sesame seeds, nuts, natural, no-sugar-added nut butters
Are there any health concerns?
As with any eating plan, the keto diet is not the best choice for everyone, Nisevich Bede says. Talk to your doctor and/or dietitian before starting, and avoid the keto diet if you:
- Have a history of eating disorders
- Have Type 1 diabetes
- Are pregnant or nursing
- Have a disease that affects the kidneys, liver, pancreas, or gallbladder
- Have had bariatric surgery
Work closely with your doctor and/or dietitian while on the keto diet since there are some potential health concerns, such as increased risk for:
- Kidney stones
- Acid reflux symptoms, due to high fat intake
- Constipation, as a result of lower fiber intake
- High LDL (bad) cholesterol, since saturated fat consumption is high
- Lack of phytonutrients and antioxidants as well as dehydration, as plant-based foods become less common
The bottom line.
Research on the keto diet in healthy populations is fairly limited and still developing. "Many of the studies used to assess weight loss on the keto diet are short term, say, six months," Hyman says, so it's TBD how long you can safely stay in ketosis. That being said, it's important to have a post-plan transition strategy.
"Yo-yo dieting has adverse health effects. This diet is very restrictive and may be very difficult to maintain long-term," Hyman says. "When the individual stops following the diet, the risk for weight regain is high."