If you want to lose fat, improve metabolism, and experience other health benefits all without giving up your favourite foods, intermittent fasting (IF) might be for you!
I’m often asked my opinion about intermittent fasting. While there’s plenty of information available, many are confused about exactly what it is, and whether it is right for them. I’ll shed a little light on this popular topic.
Intermittent fasting is just that — fasting intermittently. It’s an “eating pattern,” rather than a “diet.” That means regularly reducing eating and drinking during pre-set times. It’s controlling when you eat and drink, as opposed to what you eat and drink. Of course, knowing the many benefits of a whole food diet, I suggest making healthy choices when intermittingly fasting.
We already know that it’s really difficult to sustain a (continuous) calorie reduced diet for a long time. This is the reason why many people prefer intermittent fasting — it gets similar weight and fat loss results, plus it’s easier for many people to stick with. This makes IF a great alternative for anyone who wants to lose weight and fat, but has difficulty sticking with a reduced calorie diet.
Other advantages to IF over calorie reduced diets are that it can help people eat more intentionally (and less mindlessly).
Let’s review some of the health benefits, look at the most popular methods, and identify who shouldn’t intermittently fast.
Over and above the weight and fat loss benefits, IF has metabolic benefits and may not only help with overweight and obesity, but with metabolic syndrome, Type 2 diabetes, and heart disease as well.
People who IF sometimes have improved insulin sensitivity and blood sugar levels. They also show improved blood lipids, reduced blood pressure, and even reduced inflammatory markers. All of these are related to improved metabolism and reduced risks for many chronic diseases.
One unique way IF works is by making our metabolism more “flexible.” This is really important for blood sugar control and diabetes risk. According to an article by Harvie and Howel published in Behavioral Sciences Journal (2017), “Metabolic in flexibility is thought to be the root cause of insulin resistance.” Another article from PMC (2018) entitled “Flipping the Metabolic Switch: Understanding and Applying Health Benefits of Fasting” states that “When taken together with animal studies, the medical experience with fasting, glucose regulation and diabetes strongly suggests IF can be effective in preventing type 2 diabetes.”
Let me explain how it works. After we eat, our bodies use carbohydrates (e.g. glucose) from our food for fuel. If there is extra left over, it’s stored as fat for future use.
With fasting, our bodies flip from using glucose (and storing fat), to using that stored fat and ketones (made from fats) for fuel. The ability to flip what our bodies use as fuel (between glucose and ketones) is called “metabolic flexibility.”
It’s thought that we, and many animals, evolved to have this ability to survive short periods of fasting from when we were hunter-gatherers. There were times when people didn’t have a lot to eat, but they still needed to survive and think clearly enough to successfully find food.
This metabolic switch can explain some of the health benefits of fasting. When our bodies prefer using fats for fuel, the body starts burning our stored fat. This is how IF helps with overweight, obesity, metabolic syndrome, and type 2 diabetes. When the body uses fat for energy this decreases the amount of fat in the body. Reduced fat reduces weight, and health benefits from weight loss are felt.
This “flipping” of the metabolic “switch” happens after the available glucose, and the stored glucose are depleted. This is anywhere from 12-36 hours from the last meal, depending on the person. At this point the fats in our cells start getting released into the blood and are metabolized into ketones.
Since the body is burning fat and using ketones to fuel the muscles, IF can preserve muscle mass. Some studies of IF show that it preserves more muscle mass than regular calorie reduced diets do.
Neurons (in the brain and nervous system) are also fueled by ketones and when our neurons start using ketones for fuel, brain function is preserved, thereby supporting learning, memory, and mood. Another important benefit is resistance to stress.
Many animal studies show that intermittent fasting can help improve the ability to think and improve memory. Studies also show that alternate day fasting protects brain neurons in animal models of Alzheimer’s, Parkinson’s and stroke.
When it comes to weight and fat loss, consistently reducing the amount ingested by 15 to 60 per cent, results in loss of both weight and fat. This is called “continuous” calorie reduction because one is continuously reducing daily food and beverage intake at every meal and snack. Calorie reduced diets can include eating smaller servings, lower calorie substitutions, and/or cutting out some snacks/desserts every day.
For people who have excess weight, losing weight (and fat) reduces the risk of diabetes, improves healthy lifespan, and increases function of both the body and mind.
After about five to six per cent of a person’s body weight is lost, even more health benefits are seen. Improved LDL cholesterol and triglyceride levels, improved blood sugar levels, lowered blood pressure and lowered levels of inflammation.
Both continuous calorie reduction and IF have similar weight loss results, however, Intermittent fasting isn’t a continuous reduction, but rather an intermittent one. It allows you to eat what you want, but only during certain times. It’s an alternative to calorie reduced diets. I guess we could say that IF is a way to “diet” without “dieting.”
IF can provide a lot of health benefits, and a recent article by Patterson & Sears (2017) published in Annual Review of Nutrition states that “Overall, intermittent fasting regimens are not harmful physically or mentally in healthy, normal weight, overweight, or obese adults.”
There are a few things to keep in mind before considering intermittent fasting, and it is advisable to check with your healthcare professional before trying any major changes to your diet.
A number of adverse effects have been reported, including: bad temper, low mood, lack of concentration, feeling cold, nausea, vomiting, constipation, swelling, hair loss, muscle weakness, uric acid in the blood and reduced kidney function, menstrual irregularities, abnormal liver function tests, headaches, fainting, weakness, dehydration, mild metabolic acidosis, preoccupation with food, erratic eating patterns, binging, and hunger pangs.
If done too often or for too many days IF can have more serious effects. Excessive fasting can lead to malnutrition, decreased bone density, eating disorders, susceptibility to infectious diseases, or damage to organs.
There are several ways to intermittently fast:
Alternate-day fasting (ADF): One day of fasting, one day of “feasting.” Continue fasting on alternate days.
Alternate-day modified fasting (ADMF): Eat 25 to 40 per cent of your daily needs one day, then eat normally the next. Continue alternating days.
Periodic fasting (PF) or “Two day” fasting: Each week has 1 or 2 days to eat very few calories per day (e.g. 0-880 cal/day). The other 5 days you eat normally. Example: 5:2 diet, where you eat no more than 500 calories/day for two non-consecutive days each week.
Time-restricted fasting (TRF): Fast for 12-16 hours every day and eat normally during the other 8-12 hours.
One 24-hour period of fasting each month.
Several researchers suggest that the alternate-day modified fasting is preferable because it is likely the easiest to follow and may cause the least amount of stress on the body and mind.
Studies show that alternate-day fasting reduces overall calorie intake. Plus, on the non-restricted days, some people naturally reduce their energy intake by up to 20 to 30 per cent.
Keep in mind that reducing your food intake also reduces your nutrient intake. It’s important to ensure you get enough essential nutrients for long-term health.
In conclusion, intermittent fasting is a way to get the benefits of a regular calorie reduced diet without restricting what you eat, just when you eat it. Intermittent fasting reduces both weight and fat. It has been shown to improve blood sugar and cholesterol levels, as well as reduce blood pressure and inflammation. Many animal studies show improvements in brain health too.
While these benefits of IF are similar to those with calorie reduced diets, IF has some key advantages including being easier for some people to stick with and it might help people eat more intentionally. There is also evidence that IF preferentially reduces fat while preserving muscle and may help our bodies become more “metabolically flexible.”
More research is needed to fully understand long-term benefits of IF on the body and brain, as well as which IF approach is optimal for each individual and their health goals.
If you're interested in learning more about intermittent fasting and how it could help you reduce your risk of disease, contact me here to schedule your free 1-hour no-obligation consultation.
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