Example of some keto foods against a blue background

Weight loss: keto vs. intermittent fasting

Written on February 3, 2023 by Amy Harris, MS, RN, CNM. To give you technically accurate, evidence-based information, content published on the Everlywell blog is reviewed by credentialed professionals with expertise in medical and bioscience fields.

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Keto, intermittent fasting, paleo, warrior...what diet will be in the spotlight next? While all of these options keep the diet industry in business, they rarely answer the one question we all have: Which diet plan will help me lose weight and keep it off?

You are not alone in asking this question. Unfortunately, there is not one easy answer because everyone’s body is different. Everlywell’s new g1p1 weight loss telehealth service is committed to finding that healthy weight for every body, even yours. In this post, we’ll help you understand the pros and cons of two approaches to weight loss: keto vs. intermittent fasting.

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How are keto and intermittent fasting different?

The biggest difference between keto and intermittent fasting is that intermittent fasting diets tell you when you can eat, whereas keto diets tell you what and how much you can eat.

“Keto” is short for ketogenic, which describes when your body uses fat as its primary fuel source instead of carbohydrates (carbs). The keto diet is an extreme form of a low-carb diet, limiting you to less than 20-50 grams of carbohydrates per day (for reference, one bagel has approximately 25 grams of carbs) [1].

When you follow a ketogenic diet, you replace the calories you usually eat in carbohydrates (bread, pasta, potatoes, sugar) with calories from proteins and fats such as fatty cuts of meat, processed meats, lard, and butter.

In contrast, intermittent fasting is an eating pattern that includes hours or days with no or minimal food consumption (called fasting) interspersed with hours or days when you eat a regular diet [2]. It does not involve cutting out carbohydrates and, in fact, lets you eat your normal diet at non-fasting times.

What are the pros of the keto diet when it comes to weight loss?

Many people choose the keto diet as a “quick fix” diet — a way to quickly drop some weight, but not as a major life change. What is appealing about keto diets is that:

  • People lose more weight faster on keto [3].
  • Anecdotally, people feel less hungry following the keto diet than other ultra-restrictive or very low-calorie diets.
  • You can eat more meat-based protein and dairy-based fats [1].
  • It may do a better job of helping you burn stored body fat [4].

Research shows people tend to lose weight following a keto diet within two to three weeks, whereas it can take a month or more to see any weight change with intermittent fasting [1,4].

What are the cons of the keto diet?

Healthcare providers, nutritionists, and researchers have serious concerns about the long-term risks of following the keto diet beyond six months [4]. Not enough long-term research studies have followed humans on ketogenic diets for years at a time, although animal studies do indicate reduced disease risks and health benefits [5]. In the short term, some of the problems with the keto diet are:

  1. It is tougher to follow keto’s ultra-restrictive guidelines, making it harder to succeed or maintain.
  2. The keto diet requires cutting out multiple foods such as grains and legumes, most fruit, milk, yogurt, and many types of vegetables.
  3. Keto’s restrictions can cause vitamin and nutrient deficiencies (vitamin A, vitamin C, vitamin K, and folate, as well as dietary fiber) if followed for longer than 3-6 months [1].
  4. Eating too much protein can interfere with ketosis and weight loss success [4].
  5. Side effects can include the “keto flu”: headaches, fatigue, bad breath, muscle cramps, nausea, and constipation [4].
  6. Keto dieting can result in cyclic weight loss and gain (weight cycling) [6].

Research studies have shown that repeated fluctuations in weight (as might happen if you repeatedly stop and start the keto diet) result in a steady increase in body weight over time. They can also increase your risk for high blood pressure, gallbladder disease, and high cholesterol [6].

What are the pros of intermittent fasting plans for weight loss

Intermittent fasting is not new on the diet scene and is popular among dieters and healthcare professionals because it:

  1. Allows for a range of healthy and enjoyable foods to be eaten (less restrictive than keto)
  2. Does not require calorie counting
  3. Is flexible (there are multiple versions of intermittent fasting plans)
  4. May have long-term health benefits (blood pressure, cardiovascular risk, cholesterol level, and inflammation biomarkers) [7,8,9,10]

A systematic review of 40 studies found that intermittent fasting was effective for weight loss, with a typical loss of 7-11 pounds over 10 weeks [7].

What are the cons of intermittent fasting plans for weight loss

Fasting, even for a couple of hours, is not for everyone. Other reasons why people say no to intermittent fasting as a method of weight control are:

  1. It is not healthy for people who have diabetes or are pregnant, breastfeeding, or younger than age 18 [11].
  2. If you have trouble overeating or binge eating, overcompensating during your non-fasting times could reduce the amount of weight you lose.
  3. Long-term (longer than 5 years) health effects have not been studied [5].
  4. Weight loss may come from the loss of muscle mass and not fat [9].

The takeaway: keto for short-term losses, intermittent fasting for long-term success

Finding yourself confused by these lists of pros and cons and not sure which weight control plan is right for you?

When comparing keto vs. intermittent fasting, keep in mind that, in the short term, people tend to lose more weight quicker. That initial success can come at a high price, however, with more unpleasant side effects, potential health risks, and a greater likelihood of harmful weight cycling.

Over months and years, however, more people can successfully maintain a meaningful weight loss (5-10 percent of their original body weight) for more than a year following intermittent fasting plans [5]. The variety of intermittent fasting plans, their flexibility, and their lack of prohibiting entire food groups make them more attractive and feasible than keto diets. However, more research and time are necessary to confirm the long-term safety of intermittent fasting diet plans [2].

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When to stop a keto diet: what to know

How long should you do intermittent fasting?

What is intermittent fasting?

What is healthy weight loss?

References

  1. Schmidt, Tara. Pros and cons of a keto diet. Mayo Clinic Connect. URL. Published May 17, 2021. Accessed January 31, 2023.
  2. Diet review: intermittent fasting for weight loss. T.H. Chan Harvard School of Public Health. URL. Accessed January 31, 2023.
  3. Mohorko N, Černelič-Bizjak M, Poklar-Vatovec T, et al. Weight loss, improved physical performance, cognitive function, eating behavior, and metabolic profile in a 12-week ketogenic diet in obese adults. Nutr Res. 2019;62:64-77. doi:10.1016/j.nutres.2018.11.007. URL.
  4. Diet review: ketogenic diet for weight Loss. T.H. Chan Harvard School of Public Health. URL. Accessed January 31, 2023.
  5. Calorie restriction and fasting diets: What do we know? National Institute on Aging. Published August 4, 2018. URL. Accessed January 31, 2023.
  6. Maintaining weight loss. Johns Hopkins Medicine. URL. Accessed January 30, 2023.
  7. Seimon RV, Roekenes JA, Zibellini J, Zhu B, Gibson AA, Hills AP, Wood RE, King NA, Byrne NM, Sainsbury A. Do intermittent diets provide physiological benefits over continuous diets for weight loss? A systematic review of clinical trials. Mol Cell Endocrinol. 2015 Dec 15;418:153-72. URL.
  8. Malinowski B, Zalewska K, Węsierska A, et al. Intermittent fasting in cardiovascular disorders--an overview. Nutrients. 2019;11(3):673. URL. Published 2019 Mar 20. doi:10.3390/nu11030673.
  9. Lowe DA, Wu N, Rohdin-Bibby L, et al. Effects of time-restricted eating on weight loss and other metabolic parameters in women and men with overweight and obesity: the TREAT randomized clinical trial. JAMA Intern Med. 2020;180(11):1491–1499. doi:10.1001/jamainternmed.2020.4153. URL.
  10. Varady KA, Cienfuegos S, Ezpeleta M, Gabel K. Cardiometabolic benefits of intermittent fasting. Annual Review of Nutrition. 2021; 41:333-361. URL.
  11. Intermittent fasting: What is it and how does it work? John’s Hopkins Medicine. URL. Accessed January 31, 2023.
  12. What is intermittent fasting? Does it have health benefits? Mayo Clinic. URL. Published May 5, 2022. Accessed January 31, 2023.
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