ONE Actionable Takeaway from Ketosource

Takeaway: How Do I Choose The Best Fasting Method for Fat Loss?

Choosing a fasting method can be a challenge due to:
A) confusion over different types of fasting, and
B) little specific information on how each fast supports fat loss.

We’ve built a framework to give you clarity and help you identify the best fasting method for your situation. It’s based on a combination of our review of research studies and our experience working with clients.

What Are the Different Types of Fasting Methods?

There are six different types of fasting methods to choose from but they all have one thing in common. Each method will put you into a calorie deficit that helps you to lose fat over time.

Fasts are grouped into either short fasts (also known as intermittent), or long fasts.

  • Short fasts
    • Time Restricted Feeding (TRF): This type of fast is up to 16 or 18 hours. People who have no experience with fasting generally start here.
    • Modified Fasting: A one-day off and one-day on fasting method that allows you to intake up to 350 kcal on the days you fast. For example, a Hass avocado has about 350 kcal and would be safe to consume on your fast days. This method of fasting is also useful for those who take medications that require food.
    • Alternate-Day Fasting: This type of fast is just as it sounds. One day you fast then the next day you eat normally. This is repeated throughout the week and is usually for more experienced fasters.
    • Short-Term Fasting: A 72-hour fast that is for more experienced fasters. This type of fast is often used to help break fat loss plateaus.
  • Long Fasts
    • Fasting Mimicking Diet (5 Days): Much like the modified fasting method except prolonged for five days. Every day you can have up to 700 kcal of food and drinks.
    • Prolonged Fasting: This type of fast is longer than 72 hours or more. 

The Differences Between Fasting Methods

The main difference between fasting methods is whether you attain ketosis which depends on the length of time of your fast. The production of ketones is what helps you to feel less hungry over longer periods of time and eat less when you break your fast.

  • Short fasts (with the exception of alternate-day fasting) do not get you into ketosis.
  • Long fasts will get you into ketosis and are also useful when your fat loss progress has stalled.
  • Prolonged fasting will get you into ketosis but is not recommended for fat loss in isolation. It has been demonstrated within the research that people tend to regain much of the weight they lost when used as your sole method of fasting.

* Will possibly get you into ketosis based on your personal metabolism and keto-adaptation
* Modified fasting makes it easy to fast even when your medication requires food
* Prolonged fasts are not suggested for fat loss goals due to quick regain after completion

Choosing Your Optimum Fasting Method for Fat Loss

From working with clients we have found that the best choice is the fasting method that combines two factors:

  • First, and most important, it’s sustainable for you. Meaning you can maintain the practice without too much effort.
  • Second, it maximizes your calorie deficit.

To simplify the choice for you, we’ve developed a fasting method optimisation tool that creates your fasting method program for you. This tool leverages the framework we’ve outlined in this article, asking you a few specific questions to identify a program adapted to your situation.

Click here to use the tool to optimise your fasting for fat loss program.

When using this tool consider some of the following factors:

  • Lifestyle Fit: To make any lifestyle change sustainable we need to engineer it to work as effortlessly as possible with your existing lifestyle constraints. Examples are whether you need to take medication with food or whether you have limited windows where you can make meals. Selecting fasting methods that work with vs. against these constraints always works better.
  • Foundation vs. Sprint: Over time we’ve found that clients optimise results through a combination of fasting methods in their program. They have a foundation fasting method that is relatively effortless for them to maintain and they follow every week. Then, from time to time, when they have some additional space or willpower, they will take on a fasting sprint. A fasting sprint is where you take on a higher calorie deficit fasting method for a limited time (e.g. a day, two days or a week). While you can’t sustain the method you use with a fasting sprint, when used strategically from time to time, it is both realistic and improves your fat loss results.
  • Metabolic Experience: If you are already on a keto diet you will likely find that fasting is easier due to your metabolic adaptations and specifically your pre-existing ketone levels. The appetite-reducing ketones that you create lower your sensation of hunger allowing you to fast for longer. C8 MCT oil can be used in the same way, even if you are not on a keto diet, and keep you fasting for longer.

Actionable Takeaways

To sum up, there are many different methods but to make things easy for you to choose just remember these points:

  • The best fasting method for fat loss for you is the method that is both realistically sustainable for you, and maximizes your calorie deficit over the longer term.
  • Use our fasting method optimisation tool to design your fasting method program.
  • If you have done the keto diet before longer fasts may be easier to complete
  • C8 MCT oil can help you prolong your fast and stay satiated

ONE Quote from a Credible Expert

Takeaway: Fructose Drives Inflammation

This quote comes from Robert Lustig. Robert is Professor emeritus of Pediatrics, Division of Endocrinology at the University of California, San Francisco (UCSF). He specializes in the field of neuroendocrinology, with an emphasis on the regulation of energy balance by the central nervous system. His research and clinical practice has focused on childhood obesity and diabetes.

“Fructose is a driver of leaky gut. [It] causes inflammation at the level of the liver which ultimately leads to systemic inflammation. One of the reasons why High Sensitivity CRP is high in patients who eat ultra-processed food. And 93% of Americans today are inflamed. Does that mean that 93% of Americans have leaky gut, yeah it does.”

Source: Dr. Robert Lustig: How Sugar & Processed Foods Impact Your Health | The Huberman Lab (timestamp 01:00:18)

ONE of Your #1 Questions Answered

The Question: Can I Have Fruit on a Keto Diet?

The top question sent in from you this week was from Lizzie Hodgins. Thank you Lizzie!

“I thought Strawberries, raspberries-and blackberries are allowed [on ketogenic diets]?”

The Answer: 

Berries and other low-carb fruits are often included in a keto diet. However, based on what we see with clients, berries (or fruit in general) impede fat loss. So we recommend removing berries and all fruits from your keto diet to reach your fat loss goal.

Below we will go over why avoiding fruit is beneficial for fat loss, where there are exceptions to this rule and how to safely include them in your diet if you absolutely can’t go without them.

Why You Should Avoid Fruit on a Keto Diet

The keto diet works for fat loss by reducing your appetite. But eating too many carbs stops this from happening. Fruits are easy to overeat leading to too many carbs being consumed. If you’re not certain on how to calculate carbs, net carbs or total carbs make sure to read this article first.

For example, it is easy to eat too many carbs from fruits such as berries, apples, and oranges. There are some rare exceptions to this. Avocados, lemons, and limes are fruits that are permissible on a keto diet due to their very low carb count.

How to Safely Consume Fruit on a Keto Diet

It is not recommended to include fruit in your diet but if you really can’t go without it here are three steps to help you stay in appetite-reduction ketosis.

  • Step 1: Find out your Personal Net Carb Limit using the Personal Net Carb Calculator. Your Personal Net Carb Limit will tell you how many grams of net carbs you can have a day.
  • Step 2: Use MyFoodData database only for this (as its reliable data). Search for your fruit of interest from the database. Once you find it check the nutritional facts for the number of total carbs. (because it’s fruit, you can take the carbs amount directly, no need to calculate net carbs)
  • Step 3: Compare your Personal Net Carb Limit to the amount of total carbs in your serving of fruit. If the carbs in your serving is beneath your Personal Net Carb Limit you can have it once per day.

Actionable Takeaways

  • Avoid eating any fruit on a keto diet as it gets in the way of fat loss
  • Exceptions: Avocados, lemons and limes are keto-friendly fruits.
  • If you must have fruit be sure that the total carb count is below your Personal Net Carb Limit.


Damien Blenkinsopp MBA.

Damien is the founder of Ketosource and the host of the popular health tech/data podcast, The Quantified Body. He has an MBA from London Business School and both French (ESC) and UK 1st Class Hon. undergraduate degrees. His career has had a data-driven and analytical focus, spanning strategy consulting, market analyst and health tech/data. Damien has a passion for health, longevity and predictable results. The Quantified Body and Ketosource projects are both focused on leveraging data and analytical tools to help people get the results they want with confidence. Damien speaks 5 languages and has lived in 11 countries across 5 continents.