Can One Bite of Cake Effect Your Fat Loss?

What if I told you, it could take you over a week before your body can efficiently burn fat again after consuming 1 piece of cake. Would the cake (or any dessert) even be worth it?

Let’s step back and remind you about the role insulin has with fat storage and utilization.

Dr. Jeff Volek, an Associate Professor in the #1 ranked Department of Kinesiology at the University of Connecticut, explains:

Fat breakdown is principally controlled by a single hormone, insulin. In other words, insulin is the primary gate-keeper of body fat. If your insulin levels are consistently high, fat usage is effectively blocked. The primary nutrient that stimulates insulin is dietary carbohydrates.

This suppression of fat oxidation lasts for days after carbohydrates are consumed, not just the few hours following their digestion when insulin levels are high.

What does this mean?

It means that until your blood sugar level goes back to normal, your body stops burning fat for days after insulin was released. What is considered normal or optimal? I recommend my client get their fasting blood sugar in the mid to low 80s. Why? This is when your blood sugar is at a significant lower risk of diabetes. (Reference The Odds You Will Have Diabetes in 10 Years: What is Healthy?)

Here are 2 real life examples that I have witnessed with 2 different clients.

Example 1: Early 30-year-old client

A little background of my client. She has been battling her weight issue most of her life. She has had successes and disappointments through the years regarding releasing body fat. Overall, she is very consistent with exercise. She invested in training with me to break the shackles of being overfat. One of things I had her purchase was a blood sugar/glucose monitor which we monitored every morning, before every meal, and after ever meal to understand what foods spiked her blood sugar.

Here is her explanation of what happened.

As you know, my blood sugar was up and down for about 4 weeks--in the 100s and 90s. I was having troubles getting it to stabilize until I had two consistent weeks in a row and for 2+ weeks, my AM blood sugar was in the 80s. Then, I started to do my blood sugar before and after meals. 

On a Tuesday (last week), my lunch with a chicken salad. Before lunch, my blood sugar was 83 and an hour after eating, my blood sugar was 84. On Wednesday, I packed the exact same lunch to take with me. The difference is, that day, my office was having a birthday party, with cake. I took my blood sugar before eating the salad and it was 88. After I ate my salad, I asked "What harm could one little bite do?" I took a generous forkful of cake and threw the rest away--feeling rather virtuous. An hour later, I took my blood sugar--117!! The only difference between the two meals was a bite of cake. It then took THREE days to get back into the 80s.

Example 2: Mid-60s Diabetic Woman

A little background about my client. She has also been battling her weight issue for almost 1/2 of her life. In addition to obesity, she has struggled with depression. She became diabetic approximately 1 year prior to hiring me as her trainer. She also purchased a blood sugar/glucose monitor which we tracked every morning.

My client started training with me in June and her AM fasting blood sugar was 164. We made dietary changes and waited to see what would happen. Slowly but surely, her blood sugar improved. By September, it was down to 133. In October, it was down to 119. Keep in mind, it had been years since her blood sugar was this low! It wasn't until December that her blood sugar was 88! Coincidentally, by December, my client had lost over 50lbs of fat without ever exercising. We did all this by watching her blood sugar.

March came and her blood sugar was steadily in the 80s for most of the month. Then she asked me a question. “Could I have a piece of cake for my birthday in March? I have not cheated in over 6 months and would like to celebrate my birthday.” Since I am about progression not perfection, I said “Sure under 2 conditions. 1. You must go out to eat for the cake to ensure no seconds will be consumed. 2. You must track your fasting blood sugar prior to the cake and every day following until it goes back to your prior number.” She agreed. She checked her blood sugar prior to the cake and it was 88. She went out to a restaurant to have the cake and tested her blood sugar afterwards. It shot up to 137! As we agreed, she checked her blood sugar every morning until it got back down to 88. Here is where the story took a twist I had not anticipated. I expected the blood sugar to be high for approximately 7 days. It took 4 weeks for the blood sugar to lower to 119. It took another 5 weeks for it to hit 88. Keep in mind, my client had not cheated on her nutrition plan we had created other than a single piece of cake. It took 9 weeks before her blood sugar leveled off.

Dr. Volek explained that until your blood sugars go back to normal, you cannot burn fat.

In the previous months, my client had lost over 50lbs of fat. Guess how much fat my client lost over the 9 weeks while her blood sugar was elevated? ZERO! Absolutely nothing. My client went from joyful and optimistic to struggling to be motivated and almost depressed. One piece of cake derailed her success for over 9 weeks. Fortunately for her, she took the information she learned and applied it going forward to continue to lose body fat.

What are you to do?

One piece, or even one bike, of cake will make a difference! If you truly wonder why you are not seeing the results you expect, invest in a blood sugar/glucose monitor and track your fasting blood sugar. Understand that everyone’s metabolism is different. How your body reacts to “sugars” will be dependent on you. One client had 1 bite of cake and it haunted her fat loss for over 7 days (3 days of elevated blood sugar plus 4 days until the body relearns how to burn fat again). Another client derailed her success for over 9 weeks! When blood sugar is elevated, your body is not optimally burning fat. Even when blood sugar returns to normal, it can take additional days for the body to “relearn” how to burn fat again. While that bite of cake may be delicious, is it worth the consequence of 3 days to 9 weeks of no accomplishments of any goals?


For information on 1on1 Personal Training or Nutrition Coaching, feel free to contact me at


Steven Zahn

ACE Certified Personal Trainer

NASM Certified Personal Trainer

Pre and Post Partum Certified

Dragondoor Publications: HKC Russian Kettlebell Certified