Intermittent Fasting 15 9 Vs 16 8

Intermittent Fasting 15/9 vs 16/8

Andrew Brewer - Intermittent Fasting Expert

Written by Andrew Brewer. Updated on December 2022.

Medically reviewed and fact checked by our team.

Intermittent Fasting 15 9 Vs 16 8

When you’re fasting, you’ll start to notice changes in your body. At first, they may be so gradual. Maybe you’ll push past a hurdle and get a boost of energy. You’ll start burning fat, so in a few weeks, you’ll notice your clothes are fitting looser. Your human growth hormone levels (HGH) start to increase, helping your hair, skin, nails, and other body tissues to look and feel healthier.

You’ll get more benefits the longer you fast. While the results between 15/9 and 16/8 are similar, let’s explore the benefits of each and how they compare so you can choose.

Benefits of 15/9 Intermittent Fasting

15/9 is a variation of the tradition 16/8 fast, and you might choose this iteration because it fits better with your schedule or you have different blood sugar needs. It’s still effective, and you will notice changes in your weight, blood sugar levels, and even your cholesterol over time. You may notice feeling less tired and an overall general feeling of well being. This is because your cells have started to regenerate.

The best part of 15/9 fast is that you start to get benefits on a cellular level. Avoid snacking to get the most benefits.

Benefits of 16/8 Intermittent Fasting

16 hours is when some of the biggest benefits of intermittent fasting kick in, including increased HGH. Your body may start to enter autophagy and the beginning stages of ketosis. You will start to lose more weight as your body converts fat to energy to power its base functions. Much like in 15/9, your blood sugar levels will start to even out, the bad cholesterol on your body will drop, and your gut will be able to rest and regenerate. Fasting for 16 hours is the threshold where you start to tip the scale, both literally and figuratively.

What are the Differences?

15/9 is rarely discussed as an option in favor of the more popular 16/8. However, there are still some key differences.

  • Fasting Time

The difference in fasting time between these two intermittent fasting types is one hour. A lot happens in your body during that one hour difference, so if you can extend the fast, it’s more beneficial. If not, that’s okay. Your body will still have time to rest and recover, burning through its calories and fat stores  to help you lose weight. Your results form that aspect are similar.

  • HGH 

One of the biggest benefits of 16/8 is that your body starts to produce more HGH. HGH is a naturally occurring hormone that promotes cellular growth, so your body can start to purge dead, dying, and damaged cells. They’re replaced with new ones that will help you look and feel better. HGH will even make you look younger, giving your skin a youthful glow. 

  • Improved Sleep

Intermittent fasting can help improve your sleep, reducing your stress levels to help your body relax and recover. It’s helpful in improving your overall wellbeing. When you eat too late, your body still has to burn through the energy. During 16/8 and 15/9, you can time your meals to be early enough that your body is at its optimal rest state by bedtime. 

  • Disease Prevention

Intermittent fasting, especially 16/8 can help prevent diseases like cancer, heart disease, obesity, diabetes, and more. It will improve your longevity.

How to Choose?

As you increase your fasting windows, it’s okay to step them up incrementally. You’re not going to see a lot of difference between these two intermittent fasting plans. Yes, every hour matters when it comes to fasting; however, the step-up in benefits between 15 and 16 hours isn’t that drastic.

Andrew Brewer

Andrew Brewer

Andrew Brewer started to give people the guidance that he never received when he was first starting. His goal is to make your goals achievable and to offer you only the best fasting apps that the internet has to offer. You're not on your own - Andrew and the entire family of reviewers at are here with you every step of the way!