Understanding a High-Fat Ketogenic Diet—and is it Right for You?

Written by: the Editors of goop


Updated: November 14, 2022


Reviewed by: Dr. Sara Gottfried

Understanding a High-Fat Ketogenic Diet—and is it Right for You?

While food trends come and go, high-fat diets—lauded for their weight-loss potential and brain-function benefits—have proven to have some staying power.

Functional medicine M.D. Sara Gottfried contributes frequently to goop on the topic of weight-loss resistance. She’s spent the past two years rigorously studying the ketogenic diet—high-fat, low-carb, moderate-protein. Named for ketones, which Gottfried explains are “the energy source made by the body when there’s not enough carbohydrates to be burned for energy demand,” the goal of the diet is to get the body to burn fat instead of sugar.

Gottfried recommends the keto diet (as it’s commonly called) to help with a range of brain and focus issues—she finds ketones to be “very efficient fuel for the brain”; she also says it works well for some patients (not all) who want to lose weight but have trouble kicking sugar cravings. We talked to her about who the keto diet is right for (and whom, or when, it isn’t); the nutritional ins and outs of mastering it; and which keto-friendly meals are healthy for practically everyone, regardless of what diet we do (or don’t) practice.

A Q&A with Sara Gottfried, M.D.


What is ketosis?


In most circles, ketosis refers to nutritional ketosis, an optimized state in which you burn fat instead of sugar. Nutritional ketosis has been used to treat epilepsy since the 1920’s and its popularity for mental acuity and weight loss has surged recently. More technically, ketosis refers to a metabolic state in which most of your body’s energy comes from ketones in the blood, as opposed to glycolysis, in which energy supply comes from blood glucose. Ketones are the energy source made by the body (in the liver) when there’s not enough carbohydrates to be burned for energy demand, so the body turns to fat for energy. The body enters ketosis when blood sugar levels are below a certain level, and liver glycogen is no longer available to produce glucose for energy.

The main tenet of nutritional ketosis is to eat:
  • Fewer carbohydrates—about 5 to 10 percent

  • Protein—maximum of 20 percent

  • More healthy fat—about 60 to 80 percent of your diet

(Note that ketosis should not be confused with diabetic ketoacidosis, a dangerous state that occurs primarily in Type 1 and sometimes in Type 2 diabetics, when high levels of ketones build up because there’s not enough insulin to metabolize blood glucose—so the diabetes becomes out of control. This is sometimes due to an infection or other severe stress. But for healthy individuals without Type 1 diabetes, ketones are used as an alternative energy source and rarely poison or acidify the body.)


Why would someone want to be in nutritional ketosis? Who do you recommend it for?


Ketones are a very effective fuel for the brain—often a more efficient fuel than glucose. Your body is like a hybrid car when it comes to fuel. When you run out of carbohydrates to burn for fuel—say you’re fasting before a surgery or a religious holiday—your body seeks an alternative way to get more fuel. (If your body didn’t do this, you would die after a short fast.) So the body kicks into burning fat, which is the metabolic state of ketosis, or “keto.” Technically, your liver takes long-chain and medium-chain fatty acids from your fat tissue, and produces a major ketone called beta-hydroxybutyrate (BHB). BHB provides more energy per unit oxygen used than glucose, which benefits the brain.

I prescribe nutritional ketosis for my patients with brain and focus issues, such as: epilepsy, attention deficit, brain fog, traumatic brain injury, memory issues, mild cognitive impairment, Parkinson’s disease, and Alzheimer’s disease (including patients with one or two copies of the genes for Alzheimer’s, called ApoE4). Most of my patients on keto say they feel smarter, sharper, and more focused—and some may lose weight (fat) as a result of using ketones as fuel.


Do you recommend keto for weight loss?


Keto can promote fat loss—in the right person. For people who are sugar burners and can’t kick their sugar cravings, keto can be very helpful, because the increased fat is satisfying and curbs sugar cravings, and people eat less overall compared to their baseline diet. So, I occasionally prescribe it for weight (fat) loss, and for help with specific hormone imbalances involving insulin and stubborn fat gain because it improves insulin sensitivity. This includes patients struggling with: obesity, weight-loss resistance (assuming the thyroid is healthy), and PCOS with insulin resistance and weight gain.

Note that men respond better to low-carb and keto by becoming more sensitive to insulin. In one study, a low-carb diet led to a 37-percent reduction in insulin, which accounted for 70 percent of the male participants’ weight loss. I’m not yet convinced this is true for all women (more below).


What are the guidelines to a ketogenic diet?


The safest way to try a ketogenic diet is to discuss it first with your (trusted, collaborative, and evidence-based) doctor or other clinician. I urge my patients, readers, and coaching clients to start with a keto calculator (such as Maria Emmerich’s or Martin Ankerl’s). These calculators give you guidelines for macronutrients, i.e., the number of carbs, proteins, and fats to eat to get into ketosis—and adjust the recommendations based on age, activity level, and goals (such as weight loss or maintenance).

This is a diet that requires a fair amount of attention to macronutrient quantities in order to work. Unlike the Atkins diet, which only restricts carbs, the ketogenic diet also restricts protein based on your activity level, so that extra protein doesn’t get converted into glucose. When people first go on nutritional ketosis, they sometimes focus on getting their carbs super low (i.e., less than 20 grams per day), and that can cause hormone and mood problems, especially in women. They make up the difference with too much protein, which then converts into sugar. So if you over-restrict carbs and eat too much protein, ketosis may not work. It’s not just a certain amount of carbs you want to target, but the right combination of fat, carbs, and protein for YOU.

1. Reduce carbs. How much? The short answer is to eat 20 to 25 grams each day for weight loss, and 25 to 30 for weight maintenance. (You must use a nutrition calculator for macronutrients to get it right because thinking in terms of grams is not intuitive, and nutritional ketosis is less likely to be successful if you try to “eyeball” the amounts.) The long answer is: it depends. I encourage people to limit carbs until they are in ketosis, as confirmed with a blood ketone meter (see below), and then try increasing the amount of carbs by 5 grams to see if they stay in ketosis.

Here are a few recommendations:

  • Eat one or more pounds of vegetables per day, half raw and half cooked. Let vegetables be your primary source of carbohydrates. Steam, roast, or sauté over medium heat in coconut oil or extra virgin olive oil. Make soups.

  • Initially, avoid fruit. You can eat low-glycemic fruit like berries when you are keto-adapted (consistently in ketosis and burning fat instead of carbohydrates as your primary fuel source).

  • Avoid flour, grains, and sugar: no bread, hamburger buns, pasta, tortillas, alcohol. Replace noodles with spiralized vegetables. Learn to love cauliflower rice.

  • A quick meal: One cup of kale contains about 6 grams of carbs. Two cups of Romaine lettuce contain 3 grams of carbs. One cup of cucumber contains 4 grams of carbs. Top with your favorite protein (suggestions below), olive oil, and a squeeze of lemon juice.

Note that women with thyroid or adrenal dysregulation require more healthy carbs. In general, the optimal carbohydrate level for you can vary over the years, such as when you’re more active physically or breastfeeding or stressed. Chronically eating low carb may increase your risk of mood disorders, so I urge caution and that you work with your healthcare professional. To be safe, eat the most carbs that you can tolerate while staying in ketosis.

2. Choose the amount of protein based on your activity level. For instance, I weigh about 130 pounds and exercise (spin, hike, yoga, weight training) about six or more hours per week. Applying the keto calculator, if I want to lose weight, I should eat 20 grams of carbs, 67 grams of protein, and the rest in fat (about 119 grams). Here are my typical proteins in a day. (If you exercise more than me, you’ll need more.)

Breakfast (select one):

  • 2 eggs contain 12 grams of protein

  • 1 serving of protein powder, such as pea-protein-based, which provides high amounts of the branch-chain amino acids (BCAAs) that preserve muscle mass as you age

Lunch or dinner (select one for each meal):

  • 4 ounces of pastured chicken thigh meat (about the size of my palm) is 27 grams of protein

  • 4 ounces of sockeye salmon contains 29 grams of protein

  • 1 cup of crab meat has 21 grams of protein

  • 4 ounces of grass-fed hamburger has 22 grams of protein

In general, you want to eat the minimum amount of protein to preserve lean body mass and not overtax your kidneys. If you eat too much protein, the excess converts to glucose through a process called gluconeogenesis. You don’t want that to occur in ketosis. Instead, eat anti-inflammatory protein—at the minimum amount to preserve or build lean body mass. My favorite sources are wild-caught fish, grass-fed and -finished beef and wild meats (elk, bison, etc.), pasture-raised poultry, nuts, and seeds. Make sure fish has more selenium (which helps protect the brain) than mercury, to mitigate heavy metal toxicity. Good sources that have a safe selenium/mercury ratio include: tuna, opah, wahoo, spearfish, swordfish.

3. Eat the rest in fat, so that fat makes up 60 to 80 percent of your total calories in a day.

  • Favor plant-based whole foods, like avocados, olives, and macadamia nuts. One avocado contains 21 grams of fat. Ten macadamia nuts contain about 21 grams of fat.

  • Again, eat anti-inflammatory protein with higher fat content, like grass-fed filet mignon, and pastured chicken thighs, dark turkey meat.

  • If you make the salad I mention above with 2 tablespoons of olive oil (28 grams of fat) and 4 ounces of salmon (15 grams of fat), you’ll get about 45 grams of fat, which is a good target for a meal.

  • Avoid processed meats (like bacon), which the International Agency for Research on Cancer classifies as a carcinogen, based on 800 studies showing an association between processed meats and cancer. Many keto advocates recommend bacon at every meal—I don’t see the nutritional benefit of that.

  • Limit red meat to two to three times per week. I believe it’s better to vary your protein sources, and there’s some data to suggest that limiting saturated fat can help preserve cognitive function.


Is there benefit to everyone incorporating more keto meals into their diet?


Occasionally switching to ketosis can help with mental acuity. I do it when I’m on a work deadline.


What if keto sounds like too much work?


If this all sounds like way too much work, consider intermittent fasting. It is a simpler way to achieve cyclic ketosis and has many of the same benefits. Anecdotally, it has worked better for me for weight loss than nutritional ketosis, and has many of the same health benefits. I prefer a 16/8 or 18/6 protocol, where you confine your eating (with no change in calories) to a 6- to 8-hour window, then fast overnight. For instance, I finish eating by 6 p.m., then eat again at noon the next day. For weight loss, I recommend following this protocol two to seven days per week. [Stay tuned for more on goop.]


What about women for whom keto doesn’t seem help with weight loss resistance?


As keto grows in popularity, I see more women struggle with it. My anecdotal observation in my medical office and working with people online is that younger men seem to perform best, and better than women of all ages in nutritional ketosis. My female patients, myself included, may have more problems on keto, with their stress hormones (i.e. producing too much cortisol), thyroid function, and may even develop menstrual irregularities. Some women do fine, others may feel worse, suffer from mood issues, and can even gain weight. We are still learning more about why men fare better than women (it may be related to their higher muscle mass). Additionally, there are at least ten genes that may make a person less likely to benefit from keto.

My advice is to keep your food plan in balance—eat mostly vegetables (about 1-2 pounds per day), eat the minimum protein to preserve lean body mass, avoid processed foods and those that inflame you, and track your body composition over time. Extreme works for some people, but not for me, and not for all women. I prefer getting into ketosis via intermittent fasting, on a 16/8 protocol.


How do you know you’re in a ketogenic state?


You know you’re in ketosis by checking blood ketones with a hand-held ketone meter (a test for beta-hydroxybutyrate). A ketone meter can be purchased online for about $100-120, along with ketone test strips. You prick your finger and use a drop or two of blood to measure ketones. Aim for 0.5-3.0 mm. I use Precision Xtra, which can check for both ketones and glucose in the blood (useful if you’re overweight). Some people measure ketones in the urine or via a breath taste, but I’ve found them to be not as accurate.

Again, the safest strategy is always to work in consultation with a health care practitioner.


How long should you aim to be in a ketogenic state?


I suggest trying nutritional ketosis for 6-12 weeks and testing your blood to see if it’s a good fit. With a doctor, look at inflammation, cholesterol, adrenal, and thyroid function (more on testing below).

After you’re stable in ketosis based on blood monitoring, try adding more carbs in the form of vegetables to define your threshold.

At this point, we don’t know how long is safe to remain in ketosis. Based on the clinical trials, I recommend a trial of ketosis for up to 6 months, under the care of a knowledgeable functional medicine physician. There are some clinical trials up to 12 months, so that would be the maximum I would recommend under the watchful eyes of a collaborative professional and expert.


Are there other potential uses of keto?


Ketosis has been shown to help prevent and starve cancer cells (see studies referenced below).

Ketosis improves certain forms of cellular healing, including mitochondrial biogenesis (the making of new, bigger, and higher energy-producing mitochondria), so that your cells are stronger and have more stamina, particularly when it comes to exercise. For example, some endurance and ultra-endurance athletes believe that their performance improves in nutritional ketosis compared to sugar burning, when they have more fat than carb reserves. But because of the limited data, and available data suggesting that athletes may actually perform worse on nutritional ketosis, I do not currently recommend it for elite athletes.


What are the safety concerns around nutritional ketosis? How do you do it right?


Keto is a healthy state for some, but not all. It is most proven for epilepsy and other brain problems like Alzheimer’s, mild cognitive impairment, and Parkinson’s disease. There are more safety concerns for people trying keto for fat loss or performance. In humans, there are reports of adverse reactions to keto, including menstrual irregularities, gut dysbiosis, change in circadian rhythm, hair loss, constipation, mood disorders, and thyroid dysfunction; and in rodents, insulin resistance and nonalcoholic fatty liver.

That’s why it’s important to work with a knowledgeable clinician who can guide your experience and keep you safe. Keep asking the question, Is ketosis right for me? There’s the obvious measures to track—weight, body fat, aches and pains, and hormone symptoms. I also monitor the following in my patients on ketosis:

  • Cholesterol (with an advanced panel that includes fractionated LDL and HDL)

  • Electrolytes

  • Fasting glucose and hemoglobin A1C (like a three-month snapshot of blood sugar)

  • Inflammation (C-reactive protein, homocysteine)

  • Thyroid function (with an expanded thyroid panel, including TSH, free T3, reverse T3, free T4)

  • Sex hormones (cortisol, estrogen, progesterone, testosterone)

  • Electrolytes and minerals (sodium, potassium, magnesium, copper, zinc, selenium)

Stop ketosis if lipids shift in the wrong direction, inflammation increases over baseline, hormones become more out of whack, blood sugar worsens, electrolytes are abnormal, or fat mass increases. Replete any abnormal electrolytes or mineral levels; most people in ketosis take electrolyte supplements.


What are the common mistakes people make?


The biggest mistakes with ketosis that I see in my functional medicine practice are:

  • Not dealing first with stress and HPATG (hypothalamic–pituitary–adrenal-thyroid-gonadal axis) dysregulation. Keto may not work if you’re too stressed, which raises blood sugar and can contribute to insulin resistance. In other words, stress can kick you out of ketosis or make it very difficult to maintain a ketotic state.

  • Eating too much protein (as mentioned), which may raise blood sugar.

  • Eating too much for your genes/environment. I was guilty of this when I first tried keto in 2015. I made coffee with pastured butter and coconut oil every morning, ate bacon and other fatty meats, and promptly gained weight. Without getting too much in the weeds, you want to aim for a less-caloric ketogenic food plan, not a hypercaloric one like I did. Calories aren’t everything—hormones matter more—but you need to be paying attention and not overeat, which, obviously, can cause you to gain weight.

  • Drinking alcohol will knock you out of ketosis. Once you are keto-adapted, which takes the average person about 6-12 weeks, you may be able to have an occasional glass of wine, but it’s important to monitor blood ketones to see if you fall out of the target ketone range.

  • Lack of nutrient density. I see people who eat the same meal every day—bacon, eggs, steak, and sour cream—with not enough plant diversity. Aim for 1-2 pounds of vegetables per day, ideally 20-30 species per week.


Are there other people or conditions not suited for keto?


As always, check in with your doctor. Avoid ketosis in the following cases (note—this is not an exhaustive list): history of pancreatitis, active gallbladder disease, impaired liver function, impaired fat digestion, gastric bypass surgery, decreased gastrointestinal motility, pregnancy and lactation.

Be very cautious with ketosis if you have, or suspect you have, thyroid problems. In the thyroid studies, keto seems to lower T3 (through increased reverse T3), although it’s not clear to me that this finding is a sign of dysfunction. Lower T3 may be the mechanism by which keto spares muscle loss during weight loss.

To drill down further, there are some genetic enzyme defects that cause problems with ketosis. Here are a few of note: carnitine deficiency (primary), carnitine palmitoyltransferase (CPT) I or II deficiency, carnitine translocase deficiency, beta-oxidation defects—mitochondrial 3-hydroxy-3-methylglutaryl-CoA synthase (mHMGS) deficiency, medium-chain acyl dehydrogenase deficiency (MCAD).

Sara Gottfried, M.D. is the New York Times bestselling author of Younger, The Hormone Reset Diet, and The Hormone Cure. She’s a graduate of Harvard Medical School and MIT. You can read more of her articles on hormones and weight-loss resistance here, and learn more about her here.

The views expressed in this article intend to highlight alternative studies and induce conversation. They are the views of the author and do not necessarily represent the views of goop, and are for informational purposes only, even if and to the extent that this article features the advice of physicians and medical practitioners. This article is not, nor is it intended to be, a substitute for professional medical advice, diagnosis, or treatment, and should never be relied upon for specific medical advice.