Intermittent fasting (IF) can be an effective strategy to lose weight and body fat. But it's important to know when it will help you and when it might be harmful to you.
How long should I fast for...16, 24, 3 or 12 hrs? Will I feel tired? Will having cream in my coffee negate its effects? What is the best feeding time range? Is it bad to eat late at night even though that is still within my feeding time?
These questions (and more!) might be the kind of things you are wondering about if you're trying to use intermittent fasting to lose weight or reduce your body fat%.
But actually, the most important factors I look for when I advise my patients whether IF is going benefit them are:
What time they exercise and the type of exercise they are doing.
Their stress levels.
Exercise: What Time?
The IF method I most often recommend to my patients is the 16:8 method - i.e. fast for 16 hours and feed over 8 hours and I tell them that the best time to do high-intensity interval training (HIIT) or steady-state cardio exercise (but not weightlifting) is before their first meal of the day.
At this point, the body's blood sugar is very low, and it must resort to breaking down body fat to use for energy, a process called "lipolysis". (As a side note, the water molecule is required in this fat breakdown, so drinking enough water is key.)
However, for my patients that can only workout early in the morning, I don't recommend IF. After an intense workout, protein and carbs are needed (i.e. within 30-60 min.) to build muscle and for recovery to prepare the body for the next day's workout.
I have seen firsthand using my InBody Advanced Body Composition analysis that those who workout hard in the morning but don't eat right after and continue to fast until noon or 1 pm lose muscle mass (and also find it difficult to lose body fat). This is obviously not the kind of weight loss we want!
Cortisol is a stress hormone that has been linked glucose intolerance and insulin resistance. These are things that disable the body's ability to deal properly with the carbohydrates in food, contributing to increased abdominal/visceral fat and fatty liver.
A study in the Journal of Epidemiology (2016) looked at whether chronic stress could be used as a risk factor for insulin resistance. The results showed that the participants who were under high job stress with elevated cortisol had higher glucose (sugar) levels and abdominal circumference (i.e. higher waist-to-hip ratio). And so, measuring cortisol can be used as an indicator for insulin resistance.
I usually perform a urine test in the office to check the stress status in my patients. If it shows they're pretty overwhelmed, then I don't recommend IF to them.
You might be thinking, why? If someone has high glucose or insulin resistance, wouldn't it better for them to fast to give their body time to lower their blood sugar levels? Possibly.
However, these are some themes that I've noticed in my practice:
Fasting for too long may contribute to more stress to the body. It usually just takes 3.5-4 hours for blood sugar levels to return to normal after a meal.
Highly stressed people are often skipping meals - they are already fasting but not doing it strategically to help with improving their body composition.
Digestion is often impaired in people who are highly stressed. Therefore, eating all their calories for the day during a small time span will not be optimal for absorption of nutrients and may result in more fatigue or constipation/diarrhea.
Meals at routine, predictable times (i.e. the same times during the day) are one of the ways to reduce stress effects to the body. More protein and good fats are needed at each meal, especially at breakfast. I usually ask my patients to have their breakfast before 10 a.m. which includes protein and healthy fat, with a very small portion of complex carbohydrate.
Cortisol imbalance will cause one to crave more sugars and carbohydrates. Having timed meals throughout the day with proteins and healthy fats helps with satiety and appetite.
Highly stressed people often don't drink enough water. The water molecule is important for the breakdown of fat during fasting and so focusing on drinking more water first before trying IF is preferred.
Be well and happy,
Ref: Gur C, Boz M, Muderissoglu C, Polat H. The Relationship Between Insulin Resistance and Cortisol Levels. Istanbul Med J. 2005;16:73-76.
Yan Y, Xiao H, Wang S, et al. Investigation of the Relationship Between Chronic Stress and Insulin Resistance in a Chinese Population. J Epidemiol. 2016;26(7):355-360.