Rich LaFountain is a science writer with a passion for exploring metabolic health and athletic performance. He completed his Bachelor of Science in Biology at the College at Brockport and received his master’s and doctorate degrees in Kinesiology from the Ohio State University. Rich is fascinated by human longevity research and the science behind building diverse habits for lifelong health and wellness.

If you want to speed up your Fasting Zones, your best bet is to consume a smaller, low-carbohydrate pre-fast meal. Having a large, high-carbohydrate meal before your fast means it will take longer for you to reach Fat Burning and Ketosis Zones. 

To get a more precise picture about what’s happening in your body, we use your demographic info (sex, age, weight) along with your nutrition and physical activity to estimate your progress. Changes in your diet and nutrition can either speed up or slow down your Fasting Zones. 

How does a pre-fast meal impact your Fasting Zones?

The last meal you consume before your fast will directly impact your Fasting Zones because of the external energy it provides. Meal size and carbohydrate content are the major players here. Before your body can burn significant quantities of stored sugars and fatty acids, it will first need to absorb and burn the fuels you just consumed. 

From a blood glucose perspective, each meal you eat takes about 2-4 hours to be digested and metabolized. This “postprandial state” is influenced by the quantity and types of food you consume. All that nutrition is still being dealt with for the first few hours of a fast. Extremely large meals can take up to 6 hours to process. 

How does the macronutrient composition of your meal impact your Fasting Zones?

If you eat a high carbohydrate meal, you are going to have a more direct impact on topping off your glycogen stores than if you have a high protein or high fat meal, low in carbohydrates. If you are looking to improve efficiency, then your pre-fast meal should be a small or moderate size and low in carbohydrate.

How does meal size (Calories) make a difference?

The more Calories your meal contains, the more work your body will have to do to burn and/or store all that energy. Large meals can often increase the time your body takes to break down food as well as boosting your glycogen fuel stores. The higher your glycogen levels, the longer you will need to fast to begin shifting your fuel preference to fat. 

For example: your body could break down and burn a 350 Calorie meal in a few short hours, but a meal containing 1200 Calories would take much longer. For efficiency’s sake, at a certain point, your body will store excess Calories for later. 

What does meal size kcal look like 350 vs 350-750 vs 750+

Metabolism is incredibly personal. There are so many factors that impact how you, as an individual, process your meals. We are just beginning to scratch the surface of Fasting Zone progression, and we’re committed to continually making this feature more and more accurate, personal, and scientifically sound to help you understand what’s going on inside your body. 

Lefèbvre PJ, Scheen AJ. Glucose metabolism and the postprandial state. Eur J Clin Invest. 1999 Jun;29 Suppl 2:1-6. doi: 10.1046/j.1365-2362.1999.00003.x. PMID: 10383603.

Dimitriadis GD, Maratou E, Kountouri A, Board M, Lambadiari V. Regulation of Postabsorptive and Postprandial Glucose Metabolism by Insulin-Dependent and Insulin-Independent Mechanisms: An Integrative Approach. Nutrients. 2021 Jan 6;13(1):159. doi: 10.3390/nu13010159. PMID: 33419065; PMCID: PMC7825450.

Hultman E, Bergström J. Muscle glycogen synthesis in relation to diet studied in normal subjects. Acta Med Scand. 1967 Jul;182(1):109-17. doi: 10.1111/j.0954-6820.1967.tb11504.x. PMID: 6028947.

Katz LD, Glickman MG, Rapoport S, Ferrannini E, DeFronzo RA. Splanchnic and peripheral disposal of oral glucose in man. Diabetes. 1983 Jul;32(7):675-9. doi: 10.2337/diab.32.7.675. PMID: 6862113.

Levine JA, Eberhardt NL, Jensen MD. Role of nonexercise activity thermogenesis in resistance to fat gain in humans. Science. 1999 Jan 8;283(5399):212-4. doi: 10.1126/science.283.5399.212. PMID: 9880251.

How Your Meals Impact Your Fasting Zones

Read the rest of this article with a Zero Plus account.