Intermittent Fasting: Does When You Eat Matter More Than What You Eat?

By Caydance Rose 

Intermittent fasting has been labeled as a breakthrough in the health and wellness world, with claims that the weight loss and metabolic benefits of fasting far outweigh the benefits of standard calorie restriction. Research has been aimed at examining the metabolic and physiological benefits of a fasting regimen as opposed to standard calorie restriction. The majority of research does suggest that intermittent fasting is more than just a trend, and has been shown to positively impact weight, insulin resistance, and metabolic health in both healthy patients and those with preexisting conditions.  

What is Intermittent Fasting? 

People have been fasting for religious and spiritual purposes for years, but it has just recently gained traction in the diet community for its proposed benefits in the weight loss and metabolic health communities. Fasting differs from a traditional diet in a sense that it focuses more on when you eat vs. what you eat. Fasting allows your body to transition between fasted and fed states through various fasting intervals that are curated to fit different lifestyles and health needs.  

Common examples of intermittent fasting schedules include:  

• 16:8 Method: Reducing a daily eating window to only 8 hours, allowing for 16 hours of fast 

• 5:2 Method: Eat at maintenance for 5 days per week, and restrict calories for the remaining 2 days 

• Alternate Day Fasting (ADF): Alternate between fast and feast days. (Commonly implemented by consuming 25% of daily calories followed by 125% the next day) 

Metabolic Switching: Why Fasting Works 

Metabolic switching is a widely known benefit of intermittent fasting where the body transitions from using glucose for fuel to burning stored fat during periods of starvation. Fatty acids are converted into ketones as a source of clean energy for the body, producing less byproducts and contributing less to systemic inflammation than glucose metabolism. By switching fuel sources, fasting actually places the body into a state of stress, which might seem counterintuitive but has actually been proven to enhance metabolic performance.  

What are the Benefits of Fasting?  

Research has examined many potential benefits of intermittent fasting:  

Weight Loss: 

Physiological changes related to body mass are among the most commonly proposed benefits of intermittent fasting. An intermittent fasting regimen significantly decreases caloric intake by reducing the daily amount of time spent eating in an organized way. 

By focusing less on what you eat and more on when you eat, a calorie deficit may be maintained in a way that is better tolerated by individuals who struggle with traditional calorie restriction. Many clinicians have found that structured eating schedules may improve adherence and dietary consistency. 

The effects of different fasting schedules have been studied to determine whether one regimen produces better weight loss outcomes. Multiple studies have shown no major difference in weight loss when comparing fasting strategies such as the 5:2 method and ADF. However, research frequently reports higher dropout rates with ADF, suggesting that this regimen may be more difficult to sustain long term. 

Increased Insulin Sensitivity: 

Studies have shown that fasting can enhance the body’s ability to utilize glucose as a source of energy. 

Research has demonstrated that after fasting, more glucose is required to maintain blood sugar levels, which indicates improved insulin sensitivity.  

These changes may be especially beneficial in metabolic conditions such as type 2 diabetes, where the body becomes resistant to its own glucose, which keeps blood sugar high. Fasting can serve as an intervention that allows cells to more efficiently utilize blood glucose and, in turn, lower blood sugar. 

Cellular Repair: 

Fasting has been shown to induce various processes related to cellular repair and longevity. During a starved state, the body focuses more of its energy on cell repair and eliminating waste than cellular division, ultimately increasing the quality of functioning cells within the body.  

Fasting signals activation of AMPK (amp activated kinase) which induces autophagy, a process in which cellular components and waste are broken down and recycled. Fasting also promotes mitochondrial biogenesis, which leads to an increase in the number of mitochondria in the cell, ultimately improving energy efficiency.  

Cardiovascular Health: 

Many studies have proven that intermittent fasting can greatly improve risk factors associated with cardiovascular disease. LHD cholesterol, triglycerides, inflammatory markers, and blood pressure have all been shown to positively improve after implementation of intermittent fasting in clinical trials.  

Example Intermittent Fasting Schedule 

The most common practice for intermittent fasting is the 16:8 regimen where an eating window is reduced to 8 hours, with a fast lasting for the remaining 16 hours. 

Minor variations can be made to this schedule to fit individual needs. For example, beginners may adapt better to starting a routine of 12 hours of fast and 12 hours of feast. On the other hand, those who want to more intensely implement this routine might adopt an 18:6 schedule. 

Example of the 16:8 schedule:  

• Fasting window: 8pm-12pm 

 -   Water, tea (unsweetened)  

• Meal #1: 12pm  

• Burrito bowl with grilled chicken, grilled veggies, guacamole, and sour cream 

• Tortilla Chips 

• Mixed fruit  

• Snack: 3-4 pm 

• Protein smoothie with peanut butter, banana, whey protein, almond milk, Greek yogurt, and honey 

• Dinner: 7pm 

- Salmon, sticky rice, roasted broccoli 

Intermittent fasting and Women’s Health 

Research has been conducted on the efficacy of intermittent fasting for women. Studies have shown that hormones such as estrogen and progesterone are extremely sensitive to the stress that fasting places on the body and therefore might not be supported by a fasting regimen.  If women of menstruating age would like to try fasting, it is recommended that they only fast during menstruation and one week after menstruation, as the other phases of the menstrual cycle require more calories to support proper hormone function.  

However, this idea does not typically apply to post-menopausal women as hormones during this stage of life typically do not respond negatively to fasting. Women who are post-menopausal, especially those with T2DM or cardiovascular disease may significantly benefit from fasting.  

Is Fasting Right for Everyone?  

Fasting has been proven to carry significant health benefits. However, it may not be appropriate for everyone.  

Intermittent fasting is contraindicated in those who:  

• Are pregnant or breastfeeding 

• Suffer with or have suffered with disordered eating 

• May be at risk of hypoglycemia (such as in type one diabetes)  

As always, consulting with a physician before fasting is always recommended to minimize potential risks. Additionally, intermittent fasting is not simply a replacement for a well-balanced diet. In fact, since eating windows are reduced during fasting, patients should focus more on ensuring that they are adequately meeting their intake of whole, nutrient-dense foods during their eating window.