Improving your Metabolic Fitness with Intermittent Fasting

Intermittent fasting continues to demonstrate improvements in metabolic fitness by helping to stabilize blood glucose levels and support your body’s fat-burn mode. The higher your metabolic fitness, the less risk you have for metabolic dysfunction, which can eventually manifest as  insulin resistance, type 2 diabetes, non-alcoholic fatty liver disease, high triglycerides, heart disease, cancer and more. Fasting helps improve the function of your cells and their ability to reset themselves and remove pathogens. This is a process called autophagy. 

There are many different forms of intermittent fasting (IF). The two that I recommend most often in my private practice and My Food is Health program are time restricted eating (TRE) and a five day fasting mimicking diet (FMD). I provided a general overview of intermittent fasting in a previous article from several years ago. In this article, I am sharing more recent research findings on metabolic health, considerations for women and practical ways that you can increase fasting success. As with everything, fasting protocols should be individualized because each person has a different response.  

Distinctions of Intermittent Fasting vs. Time Restricted Eating 

Intermittent fasting as a whole can be defined by three pillars: caloric restriction, variable fasting frequency (daily, weekly, monthly), and it is not necessarily intended to support the circadian rhythm. One example of this is called ProLon. ProLon is a five day fasting mimicking diet (FMD) that induces a state of autophagy, the body’s ability to reset cells and remove damaged calls of pathogens. The program includes short-term caloric deprivation (about 800 calories per day), fasting frequency of five days straight, and no specific time cutoff for your eating window. I recommend that most people complete a five day fasting mimicking diet at least once to reset their taste preferences and decision-making ability, contributing to improved metabolic health. 

Time restricted eating is defined by: no caloric restriction, practiced daily or almost daily, and supports circadian rhythm. As humans, we are built to eat during the day and rest and rejuvenate during the night. All cells in the body have their own clocks that control metabolism, the ability to process sugars and the release of hormones. Restricting the time that you eat can help prevent erratic eating at all hours of the day and night, further supporting stable blood glucose levels. This tends to work well for individuals who are not exercising intensely in the early morning, those who are trying to improve their blood sugar or blood pressure levels. The common window of fasting could be anywhere from 12-16 hours. The window that works best for you will depend on your stress levels, exercise, gender, and overall dietary habits. 

Potential Benefits of IF and TRE

Intermittent fasting and time restricted eating may contribute to:

  • Weight loss (1, 2, 3, 4, 5
  • Better blood sugar regulation (1, 2, 3, 4)
  • Lower levels of chronic inflammation (1)
  • Better cognitive function/decreased risk of Alzheimer’s Disease (1, 2, 3)
  • Improved gut microbiome & gut-immune health (1, 2
  • Reduced cancer risk (1, 2)
  • Increased longevity (1)
  • Reduction of metabolic syndrome markers (this study found this to be true, but it was not more effective than traditional continuous calorie restriction)

Research on the Fasting Mimicking Diet (FMD)

ProLon, the five day fasting mimicking diet, developed by Dr. Valter Longo and other PhD researchers from USC promotes cell rejuvenation, longevity and metabolic health. They have conducted a few studies. In one of their clinical trials, they found: 

  • IGF-1, a marker associated with aging and increased risk of cancer in mid-aged adults, was reduced by 13%.
  • Participants experienced more than a 1-inch loss in waist circumference, while lean body mass was preserved.
  • In overweight participants (BMl>25), abdominal fat was reduced by >7%.
  • Weight loss came mostly from abdominal fat (a primary predictive factor for chronic disease). Participants lost an average of 5 lbs.
  • Another study done in mice found this may be an effective intervention for inflammatory bowel disease and inducing positive changes in the microbiome.
  • This literature review explores the anti-inflammatory effects and the potential for mitigating the progression of autoimmune diseases.

Research on Time Restricted Eating (TRE)

Time restricted eating researcher, Dr. Satchin Panda and his team published a study in January 2020 that was conducted in 19 adults who had metabolic syndrome (a combination of elevations in blood sugar, triglycerides, blood pressure, waist circumference, and lipids). They fasted for 14 hours overnight and ate all meals within a 10 hour window, with the exception of water, for 12 weeks. They were not advised on decreasing caloric intake or increasing physical activity. They found that participants had a 3-4 percent reduction in body weight, abdominal fat and waist circumference; reduced blood pressure and total cholesterol and improvements in blood glucose trends. Future research that also includes a control group will help to better understand the true impact. 

Considerations for Getting Started with Fasting Mimicking Diet

1. Work with a Healthcare Practitioner 

While ProLon is very beneficial for a large number of individuals, it’s always best to work with a healthcare practitioner on implementation. This will ensure that it is a safe option for you based on your health history, current health needs  and/or history of disordered eating. The Institute for Functional Medicine notes that there are some pre-existing conditions such as kidney dysfunction or cardiac instability that will likely rule out a fast. 

2. Try to Do it With Others

We implement ProLon at specific times of the year so that a group of our clients are able to experience the program together. In my shared nutrition program, My Food is Health, all members do ProLon together during the third week of the ten week program to help induce a state of cell reset and better control blood sugar levels. Our members love being supported by others and really benefit from the power of the community support. 

3. Plan your Schedule Around the Week of ProLon 

It’s best to plan in advance to ensure that you do not have work dinners or social gatherings that are centered around food. We recommend carving out time for plenty of rest and sleep, as ProLon is an energy requiring process. 

Considerations for Getting Started with Time Restricted Eating

1. Stop Eating Earlier in the Evening 

Rather than waiting until 12pm the next day to eat for the first time, it appears to be more beneficial to cut off your eating window earlier in the evening, when possible. This allows you to break your fast earlier the next day rather than skipping breakfast. Try to eat an earlier dinner and stop eating 2-3 hours before bedtime. This is an optimal way to sync your eating with your natural biological clock, your circadian rhythm. 

During your fasting window, you can have non-caloric beverages including water, coffee, and tea without breaking your fast. In the morning, try organic black coffee, green tea or herbal tea. Adequate hydration is key for having great outcomes.  

2. Start with a 12 Hour Fasting Window

I recommend starting slow and committing to a 12 hour fasting schedule and a 12 hour eating schedule to start. For example, this would mean no food or drinks from 8pm until 8am, except for water. 

You may choose to gradually lengthen your window of fasting to 14-16 hours and pay attention to how you feel. If you have high levels of stress, exercise a lot, have low percent body fat and also eat a low carbohydrate diet, you may experience adverse effects from pushing your fasting window too long. In my clinical experience, adverse symptoms include fatigue, poor recovery from workouts, anxiety, and heart palpitations. I find that a 14:10 hour window tends to work best for women and a 16:8 window often works well for men. But I would highly recommend working with a registered dietitian or doctor to refine this window. 

Try to start time restricted eating 3-4 days per week versus everyday. You will still get benefits from some fasting compared to no fasting. Also consider taking 1-2 days off of TRE and eating a little earlier than usual to help decrease stress on the adrenals and improve metabolic flexibility. 

3. Women Should Especially Consider Starting Slow 

Women are more susceptible to hormonal, adrenal and thyroid fluctuations than men due to having a larger hormonal framework that can be disrupted by additional stressors. Additionally, most of the fasting research has been conducted in men. One cross-sectional study conducted in women found that every 3-hour increase in nighttime fasting was associated with 20% lower odds of elevated HbA1c (three month average blood glucose). So intermittent fasting can still be beneficial for women, but effects appear to be less pronounced compared to men. Despite the limited research that exists, in my clinical practice, women can benefit from TRE if they do not push it too long. 

4. Consider Getting your Cortisol Levels Tested

While fasting and TRE have benefits, they are both hormetic stressors and can increase cortisol production. If you have a lot of stress in your life and/or HPA Axis Dysfunction then this can lead to higher cortisol production. Consequences of this include changes in sex hormones, decreased conversion of thyroid hormone T4 to T3, insomnia, brain fog, anxiety, fatigue and heart palpitations. Prior to incorporating long-term aggressive time restricted eating or fasting, consider working with a practitioner to check your cortisol levels. Be sure to prioritize sleep and stress reduction techniques.

This study found increased cortisol levels from baseline with fasting, but levels normalized after a few weeks of following the eating pattern. However, the study suggested that, “caloric restriction overall significantly increased serum cortisol, an effect which is attributable to fasting rather than VLCD (very low calorie diet) or other less intense low calorie diets.” 

5. Add Herbal Teas in the Evening 

Herbal teas can provide lots of incredible flavors without interfering with the fasting window since they are typically very low in calories and do not contain added sugars. Try to drink herbal tea in the evening to reduce any food temptations that you may experience.  

Herbal tea suggestions: 

  • Crave sweets? Try cinnamon or rooibos tea
  • Digestive issues like IBS? Try peppermint or ginger tea
  • Hormonal issues like PCOS? Try spearmint tea
  • Trouble with insomnia or anxiety? Try chamomile or lavender tea 
  • Want to make your own anti-inflammatory blend? Try my recipe here

Look for tea that is USDA organic – a good example is the Traditional Medicinal brand, which is organic and has tea bags made from hemp and wood pulp, meaning they are naturally gluten-free and do not contain any micro plastics.

When drinking tea during your fasting window, it’s best to consume without honey or other sweeteners to prevent you from disrupting the fast. I also do not recommend non-caloric sweeteners (including monk fruit or stevia) during the fast. Intermittent fasting expert, Dr. Jason Fung explains that non-nutritive sweeteners may still disrupt the liver and will not help with breaking cravings.

6. Pay Attention to your Hunger Levels and Cravings 

For many people, intermittent fasting helps decrease cravings but for some, it may increase the desire to eat. This is thought to be associated with a person’s genetics. If you have a genetic mutation that makes you more susceptible or prior history of binge eating, you may overeat/binge during your eating window. This can lead to low energy, possible weight gain, bloating, and decreased sensitivity to hunger/fullness cues. Stick with a 12 hour fast if you notice increased cravings or overeating with longer fasting windows.

7. Flex your Window for Sustainability 

The incredible thing about time restricted eating is that it can be very flexible to your work schedule. If you have a late work dinner one night and don’t finish eating until 9pm, you can flex your window and wait until 9am or 11am (for a 12 hour or 14 hour fast respectively) to eat the next day. The same thing can be applied to a breakfast meeting at 8am – try to eat an earlier dinner the night before around 5pm or 7pm (14 hour or 12 hour fast).

8. Factor in Your Workouts 

It’s best to eat within 30-60 minutes of a workout to increase muscle synthesis. Adding an early morning post-workout recovery meal can make it difficult to also fast for at least 12 hours overnight. For example, if your morning workout ends at 6:30am, then it’s best to eat a protein and intact carbohydrate by 7:30am. But the problem occurs if you finished eating at 8pm the night before and you do not want to break fast until 8am. 

There are a few ways to get around this. On nights prior to your morning workouts, try to eat an earlier dinner. You can also make the days that you do not workout in the mornings your longer overnight fasts. But it’s best to factor in your early morning workouts, how often they occur each week, how early you are able to have dinner the night before, and which days will be your longer fasts. This is where planning at the beginning of the week is critical for success. 

Lastly, more is not always better. When it comes to fasting, there appears to be a point of diminishing return, which will vary for every person. Pushing your TRE window too far (especially >16 hours) may lead to fatigue, sluggish digestion, brain fog, elevated glucose levels, and other side effects. 

Photo by Claudia Crespo on Unsplash