You’ve probably heard of the ketogenic or keto diet, the high-fat, low-carb philosophy thanks to its contributions to weight loss, anti-inflammatory benefits, and improved health and well-being. These seemingly magical effects aren't magic at all: they're a simple result of the way the keto diet trains your body to get its energy not from glucose, but rather from ketones, which are produced by the liver when there is no glucose to be had.
While the idea is simple, getting your body into a ketogenic state can be more complex. To force the body to use ketones instead of glucose, carbs need to be severely limited, and the body needs to go through a period of transition, in order to learn to get its energy from this alternate source.
According to our experts, getting into a ketogenic state takes an average of about two days to two weeks, depending on the person and the diet they were consuming before they started. But it’s especially interesting to note that unlike other elimination diets, when it comes to keto, once you’ve made the leap, falling off the wagon, as such, is not that big a deal.
Kristen Mancinelli, registered dietitian and author of "The Ketogenic Diet", explains that after an initial transition period, cycling in and out of ketosis becomes much easier.
“You become what’s called very ‘metabolically flexible,’” she explains, “which is that your cells can use glucose, they can use fatty acids, and they can switch between the two; it’s not a problem.”
“You don't need to be in ketosis for the rest of your life every day,” she continues. “That's not necessarily the goal. Coming in and out is good; metabolic flexibility is good.”
Dr. Josh Axe, D.N.M., C.N.S., D.C., founder of Ancient Nutrition and DrAxe.com, notes that someone who has come out of ketosis can get right back into the coveted state by increasing their fat intake, drastically reducing carbs, fasting, or exercising.
“Ketosis involves the depletion of glycogen stores, which is why you lose so much water weight when you begin the diet (glycogen requires three times its weight in water to hang out in your cells),” he explains. “By exercising, you can speed up your glycogen depletion, leading to ketosis.”
Drew Manning, creator of the 60-Day Keto Jumpstart and Fit2Fat2Fit, notes that using intermittent fasting (seen as part and parcel of the keto diet by many practitioners) is one of the easiest ways to get into ketosis, for the first or the hundredth time.
"Our body's natural backup system is to kick into a state of ketosis," he explains. "Intermittent fasting plus a ketogenic diet has a synergistic effect, so you can get into ketosis quicker, and people see better results.”
Of course, to ensure that your body does have something to burn, cutting carbs isn’t the only part of the program: you also need to up your fat intake. This, explains Shawn Mynar NTP, CPT, RWP, Keto Nutritionist, is actually the part most people struggle with.
“If you don’t do that,” she warns, “you just significantly lower your carbohydrates, and then you’re in low-carb purgatory. You’re not providing the glucose your body is using for fuel, but you’re also not producing ketones, so your body doesn’t even know what to burn.”
The key, then, is balance: adding enough fat for your body to produce ketones, and reducing your carbs enough so that your body consumes those ketones instead of glucose for energy.
As for how many carbs that adds up to, that will all depend on three major factors.
1. What kind of carbs do you eat on the keto diet?
Like with other low-carb diets, the keto diet seeks to reduce your carbs drastically – but you can’t cut them out entirely, either.
“You’d likely be lowering your carbs pretty significantly, even in comparison to if you were already doing a low-carb diet,” explains Mynar. “But does it have to be zero? Definitely not.”
Carbohydrates are present in everything from grains to fruits to vegetables. Even protein can eventually be converted into glucose, which means the keto diet also limits protein – about two times as many grams as carbs, according to Dr. Axe.
But while some people take the high-fat element of keto to heart, making "fat bombs" of high-fat dairy and nut butter (sweetened with fake sugar) that essentially amount to junk food, a healthful keto diet isn’t just about eating as much fat as possible – it’s about pairing large quantities of healthful fat with nutrient-dense, carb-poor whole foods.
“I very much promote a real food, nutrient-dense kind of keto diet,” says Mynar, “which means you’re going to be eating lots of vegetables.”
Like grains and sugar, vegetables do contain carbohydrates; they also, however, contain essential vitamins, minerals, and phytonutrients.
“I always cringe when people jump into the keto diet and stop eating fruits and veggies and starting feasting on mountains of cheese and bacon,” says Audrey Christie, MSN, RN, CCMA, Holistic Wellness Practitioner. “Veggies are critical to health, well-being, muscle building and a whole host of things.”
For Dr. Luiza Petre, a board-certified cardiologist with extensive training and experience in healthy diet and weight loss, the key is choosing foods that are rich in fiber, which don’t spike blood sugar levels the same way that simple carbohydrates, like sugar, do.
She suggests including high-fiber vegetables, like artichokes, sweet peas, parsnips, and okra, in moderation. To that list, Christie adds leafy greens, like spinach, kale, and romaine; Mancinelli notes that these bring essential B vitamins to your diet, which most non-keto-eaters get from grains, a keto diet no-no.
“You can still eat what I call 'medium-starchy' vegetables on the ketogenic diet,” explains Dr. Axe. “These include sweet peas, artichokes, okra, carrots, beets, parsnips, sweet potatoes, yams and white potatoes. In addition, it’s okay to add in some healthy legumes/beans like chickpeas, kidney, lima, black and brown beans or lentils, hummus, etc."
It’s also important to be aware of your consumption of certain minerals, like sodium, magnesium, and potassium.
“When the body switches from burning carbs to fat, the kidneys also switch from retaining sodium to excreting sodium and other minerals, such as magnesium,” says Catherine Metzgar, Ph.D, RD, an expert of nutritional biochemistry and a member of the health coach clinical team at Vira Health.
Between three and seven grams of sodium a day is ideal, according to our experts; this can come from sea salt or pink Himalayan salt. Petre also recommends eating almonds, spinach, and pumpkin seeds for added magnesium and avocados for potassium.
Most of our experts recommend supplementing as well: Petre suggests a daily multivitamin, while Manning recommends between 300 to 500 mg of magnesium citrate or magnesium glycinate and around 1300 to 3500 mg of potassium citrate.
Drinking lots of water is also key, as dehydration can be a side effect of the keto diet. Petre says suggests 2.5 liters a day to help with the headaches and constipation that can be linked to the early stages of the keto diet.
Finally, fermented foods are essential to good digestive health when on keto. Manning suggests kimchi or sauerkraut in addition to probiotics.
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“Sometimes people don't get enough fiber or they're not getting in enough pre- and probiotics from these types of foods, so supplementing can definitely help out,” he says.
Of course, this is just a baseline: as Manning notes, there is “no one-size-fits-all approach to keto.”
“It's very bioindividual,” he says, noting that some people can eat certain carb-rich foods, like sweet potatoes, and remain in ketosis where others cannot.
Some foods that might work for some people but not for others include berries and melon, both of which are high in fiber but also in sugar. Some high-fat foods, Mancinelli notes, like dairy, nuts, and seeds, might be inflammatory for some people but not for others.
But while the focus should be on healthful, nutrient-rich carbs, the point of the keto diet is to reduce carbs as much as possible, Mancinelli explains.
"I don't really have an example of foods that are richer in carbs to have on keto, because the point of keto is to not have carbs," she says.
This, explains Metzgar, is particularly important for people living with type 2 diabetes or another variant of insulin resistance. For these people, she says, "it's likely that carb-rich food options are not appropriate to add to their regular intake.”
“Younger, metabolically healthier, and more active individuals are more likely able to tolerate some carb-rich foods from time to time,” she continues.
2. Net carbs or total carbs?
Many keto experts estimate the ideal carb intake on the keto diet at around 20 grams of net carbs, which is defined as the food's total grams of carbohydrates minus grams of fiber. To hit that level, you'll need to use a calorie counting app to calculate the exact net carbs you're consuming every day.
Dr. Axe recommends starting with a “Feast Phase,” where for three days, you include much more fat in your diet without restricting carbs or protein.
“After that initial three-day process, I then recommend adjusting your macros to fit within a fully ketogenic diet," he says. "Typically, this means getting 60-75 percent of your calories from high-quality fats, 20-30 percent from protein and 5-10 percent from carbohydrates.”
While the exact number of net carbs will vary, most people will settle into a range of between 20 and 50 net carbs per day.
“Many people find that women do well with 20-30 grams per day, and men typically want to stick with 30-50 (unless you’re drastically cutting calories),” continues Dr. Axe.
Christie suggests not cutting back all at once, but rather reducing net carbs slowly, starting with 100 grams.
“I feel that small and sustainable shifts to lower carbs are more effective and last longer than jumping from a normal standard diet which is typically 100+ carbs in a meal to less than 20 carbs per day.”
Making this jump too quickly can also lead to the “keto flu,” a period when you feel tired and lethargic as your body searches for energy. Mancinelli remembers her first keto flu vividly, though she prefers to call it a transition, as the feelings stem from the body transitioning from a carb-based metabolism to a fat-based metabolism.
“There were a couple of days in there where you almost literally feel like your body doesn't have energy," she says. "It's hard to lift your legs to go up the stairs, your arms, like you feel very lethargic, because you are literally not getting energy that you need.”
But Mynar warns against fixating on a “magic number,” as the right carb intake varies from person to person. And unlike many, she doesn’t buy into the idea of “net carbs.”
“First of all, it adds more calculations than are necessary," she says. "And second of all, some people do have a blood sugar that reacts to fiber.”
Instead of 20 net carbs, she recommends starting at around 40 to 50 total carbs and trying to find your sweet spot from there.
3. Count it or feel it?
Strict carb targets are just jumping off point: everyone has their own keto diet carb tolerance that they need to find on their own. While most of our experts recommend starting by counting grams of carbs religiously – be they net or total – they also note that you won’t be tied to your calorie counting app forever.
Manning recommends sticking to a very low number religiously for about 60 days, after which, as the body becomes more efficient at using ketones, individuals can start to consume more carbs. How many will depend on many factors, such as lean muscle mass, fitness level, and insulin tolerance.
“Everyone's so different that you have to find your own sweet spot,” says Mynar. “It's something that everyone has the ability to learn for themselves.”
Two methods of discovering your own carb allowance prevail: one is the ketone monitor, which measures ketones in the blood, urine, or breath. (For more information on this, check out our forthcoming guide to the best way to monitor ketones.)
But while this can be a good guideline, most of our experts recommend instead learning to listen to your body.
“Carb tolerance is very individualistic," says Petre. "Ruling out medical conditions, trial and error and how you are feeling is the best indicator."
To figure out where you stand once you've cut back to the bare minimum, Mynar recommends experimenting with slightly carb-rich foods, like half a sweet potato with an otherwise keto-friendly dinner. A few hours later, test your ketones with a ketone monitor, or take note of how you're feeling to see if you're still in ketosis.
By experimenting with different foods in this way, you'll soon be able to manage a keto diet without the need to be married to your ketone monitor and calorie counting app – and that will make the diet all the more sustainable, according to Stacy Tucker, nutrition expert and RN with Almeda Labs.
“Keep it really simple, keep it really, really simple," she suggests. “This is just a lifestyle. This is just a good, healthy, balanced way to eat.”
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