Intermittent Fasting and Fat Loss

Intermittent Fasting & Fat Loss

By: Tom Franclemont | Macros Inc. Coach

What is Intermittent Fasting?

Intermittent Fasting (IF), sometimes known as Time Restricted Feeding (TRF), refers to eating only within a shortened period of the day, typically within a window ranging from 4 to 8 hours in length (1).  This strategy is usually used by people who are looking to lose body fat and can be suitable for individuals who prefer fewer, larger meals or those who have a daily schedule that makes a shorter eating window more preferable.

Intermittent Fasting and Overdraft Protection: an Analogy

Let’s talk for a moment about bank accounts.  I am a member of a credit union and have free overdraft transfers from my savings account to my checking account.  Imagine that I start the month with $100,000 in my savings.  Even though all transactions are made through my checking account, there is no need for me to keep a balance there, since it is automatically moved over from my savings when necessary.  Let’s say that I also have an automatic debit of $100 per day scheduled to be taken from my checking account.  Over the course of the month, I’m going to spend $3,000 on these debits, regardless of when or how much I deposit into my account throughout the month.

Scenario #1: Starting on the 1st of the month, the daily $100 is being deducted from my account every day.  Since there is no money in my checking account, the overdraft transfer automatically pulls $100 from my savings account each day to cover the transaction.  On the 6th, I make my first deposit and add $350 to my checking account.  That deposit will cover the daily deductions for a few days and an overdraft transfer won’t need to take place again until the 9th.  On the 11th, I make another deposit, but this time $500 so it will last a bit longer.  Before that deposit has been fully withdrawn from my checking account, I deposit another $250 on the 15th.  A few days later on the 18th, I deposit $600 and finish my deposits with a final $300 on the 21st, bringing my total contributions to $2,000 for the month.  However, this is $1,000 less than the sum of the automatic daily withdrawals, so my balance is down to $99,000 to end the month.

Scenario #2: Again, the automatic withdrawals begin on the 1st of the month.  This time, I don’t have a chance to go to the bank until the 11th, so I make a larger deposit of $650, knowing that the month is almost half over already.  On the 17th, I add $900 more to my checking account.  Since I’m making larger deposits, the overdraft transfers are needed less often because there is a balance in my checking account to draw from.  Finally, I deposit $450 on the 20th to again bring my total deposits to $2,000 for the month, but again finishing with just $99,000 in my savings account.

The Effectiveness of Intermittent Fasting for Losing Fat

So what does a bank account have to do with intermittent fasting and fat loss?  Your body starts each day with a certain energy balance, its body fat stores (your savings account).  No matter how lean you are, there’s always some there, or else you’d be dead.  Through the day, you will use that stored energy to cover expenditures when your energy balance (checking account) comes up short.  When you eat, you add more energy to your system, just like depositing money into your checking account to cover your expenses.  But at times, your body will need to make an overdraft transfer from your savings account when there isn’t enough available in your checking account.

Each of those deposits represented calories in.  In scenario #1, there was breakfast at 6 AM, lunch at 11, a snack at 3, dinner at 6, and another snack at 9 PM to end the day.  For scenario #2, lunch was delayed until noon, followed by dinner at 5 PM, and a snack at 8 PM to keep all eating within an 8-hour window.  In both cases though, a total of 2,000 calories was consumed over the course of the day.  At the same time, your body is continuously burning calories just to stay alive.  This was the $100 withdrawals, which simulated Total Daily Energy Expenditure.  Even though TDEE doesn’t occur at a constant rate throughout the day, we kept it simple for this comparison, and this came to a total of 3,000 calories out, creating an overall deficit of 1,000 calories that needed to be “spent” from the savings account of stored body fat.

Fasting and weight loss

By waiting until later in the day to start eating, more energy was taken from body fat stores initially because energy hadn’t been added yet.  However, when the higher calorie meals were eaten during the shorter window, a larger amount of extra energy is available to replenish what was burned early in the day.  As you can see, at one point enough calories had been consumed during the IF window that energy balance was back to maintenance briefly.

Similarly, if training was completed prior to the first meal of the day, this “fasted training” would burn more stored fat during the exercise session, but would not result in greater total fat loss for the day in comparison to training during the eating window (2,3).


Fat oxidation and fat storage are biological processes that occur continuously throughout the day.  In order to lose body fat, your body needs to store less fat over time than it oxidizes for energy, which means that you need to be in a net calorie deficit.  Intermittent Fasting is simply a tool that can be utilized for managing hunger and calorie intake throughout the day.  There are no inherent fat loss benefits to eating during a smaller portion of the day when compared to an equal calorie intake spread across a longer period of time (4).  If your goal is to lose body fat, choose an eating schedule that will allow you to adhere to your calorie allowance for the day.