What is intermittent fasting?
There are so many different diets out there that claim to help with weight loss and disease prevention: low-fat, low-carb, ketogenic, paleo, whole 30, vegetarian, vegan, DASH, etc. But I want to talk about one of the latest trends: intermittent fasting.
You may be used to eating three meals every day, plus snacks. That’s pretty common. With intermittent fasting you can essentially eat how much of whatever you want—but here’s the catch: you have to stay on schedule. With intermittent fasting, there are scheduled periods of time when you can eat and others when you have to fast. Unlike most other diets, intermittent fasting tells you when to eat, not what to eat.
And, many people say that it can help lead you to better health and longer life. Sound interesting? Let’s dive into some of the pros and cons of intermittent fasting.
How to intermittent fast
Most of the diets that help achieve weight loss work by reducing the number of calories consumed. Intermittent fasting does the same thing but in a different way. This way of eating significantly limits calories (requiring fasting) BUT for certain durations of time (intermittently), while allowing little or no restrictions the rest of the time.
Intermittent fasting essentially means not eating for certain periods of time in the day. This may include skipping meals on a regular basis, sometimes daily, weekly, or monthly. Here are a few different approaches:
● Time-restricted feeding—Having all of your meals during an 8 to 12 hour window each day, drinking only water the rest of the day.
● Alternate day fasting—Eating normally one day but only a minimal amount of calories the next; alternating between “feast” days and “fast” days.
● 5:2 eating pattern—Consuming meals regularly for five days per week, then restricting to no more than 600 calories per day for the other two. This happens by eating very little and drinking only water on those two fasting days.
● Periodic fasting—Caloric intake is restricted for several consecutive days and unrestricted on all other days. For example, fasting for five straight days per month.
Benefits of intermittent fasting
Studies show that intermittent fasting can achieve weight loss. The success is similar to other diets.
Overall, research on the effect of intermittent fasting on people’s health is still emerging as to whether, in addition to some weight loss for some people, it can also prevent disease or slow down aging.
Most of the research on calorie restriction and intermittent fasting have been conducted in cells (e.g., yeasts), rodents, and even monkeys. Some, but not all of these studies show it may help to build exercise endurance, immune function, and live longer. It also seems to help resist some diseases like diabetes, heart disease, certain cancers, and Alzheimer’s.
When it comes to clinical studies (those done in people) on intermittent fasting, most have been pretty short—a few months or less. But, what we know so far is that it may help with markers of inflammation (C-reactive protein), diabetes (blood glucose levels and insulin sensitivity), and help to reduce high blood pressure and cholesterol.
When it comes to weight loss, intermittently fasting seems to work just as well as some other diets. Researchers think that eating this way decreases appetite for some people by slowing down the body’s metabolism. With a smaller appetite, you simply eat less and that is going to help you lose weight. This approach also has your body release little to no insulin during your fasting. Which helps the body release fat instead of store fat when there is excess insulin.
When we don’t take in calories in a specific time frame, our body starts using up stored carbohydrates called glycogen. The liver stores enough glycogen to last about 12 to 16 hours before it runs out of fuel. Beyond 16 hours, the body switches fuels and begins to use fat as an energy source.
At this time, our metabolism shifts from a carbohydrate-burning state to a fat-burning state. Some of the fat is used directly as fuel, while some are metabolized into biochemicals called ketones. This new fat-burning metabolic state is called ketosis. This is very different than ketoacidosis that happens in type one diabetics. The state of ketosis brings on other changes throughout the body. It’s these changes that are thought to underlie some of the other health benefits seen with intermittent fasting.
Ketones are said to be a more efficient source of energy for our bodies than glucose is and so they can help keep many of our cells working well even during periods of fasting. This is particularly true for brain cells and this may be part of the reason some animal studies show protection against age-related declines like Alzheimer’s.
Ketones may also help to ward off some cancers and inflammatory diseases like arthritis and other autoimmune diseases. They are also thought to reduce the amount of insulin in the blood which may help protect against type 2 diabetes.
On a more scientific level, intermittent fasting may extend lifespan in animals because of its effect on the DNA in our genes. Over time as we age, the way our genes are switched on and off changes. It appears that, in animals, restricting calories may slow down these age-related changes and help them to live a bit longer.
Before you start intermittently fasting
As with all major dietary changes, be sure to discuss them with your healthcare professional or book a consultation with me HERE.
Before considering intermittent fasting, know that there are certain conditions that can make it dangerous. For example, if you have diabetes you need to eat regularly to maintain your blood sugar levels, you must work with a healthcare professional before starting intermittent fasting. Also, if you’re taking certain medications like diuretics for high blood pressure or heart disease, intermittent fasting increases your risk for electrolyte abnormalities. Again you must speak with your Health professionals before starting intermittent fasting.
Intermittent fasting is not recommended for anyone who is under 18, has a history of eating disorders, or anyone who may be pregnant or breastfeeding.
Of course, whenever you change your diet you may experience side effects. Some side effects of people who restrict their calories or start intermittently fasting include fatigue, weakness, headache, reductions in sexual interest, and a reduced ability to maintain body temperature in cold environments.
Beyond the health risks and side effects, fasting simply may be hard to do voluntarily—especially when it’s for two or more days. Some people may have a natural tendency to indulge too much on their “feast” days which can negate some of the benefits of fasting. If this is the case you may want to reconsider your style of intermittent fasting.
According to the National Institutes of Health, “More research will be needed to determine the long-term impact of the diet on human health and provide information on when and how such a diet might be applied.”
Nutrition tips for intermittent fasting
Intermittent fasting can be hard. One thing that can help is having a social support network—especially for those days when you’re fasting.
Although the premise of intermittent fasting is to restrict when you eat, not what you eat, the quality of your food choices is still very important. Regardless of your eating style and preferences, you still need all of your essential nutrients. Intermittent fasting is not a good reason to eat a lot of the high-calorie nutrient-poor foods we all sometimes crave. I recommend eating adequate amounts of lean proteins, healthy fats, fruits, a lot of vegetables, legumes, and whole grains. Also, avoid too many sugars and refined grains.
The main reason for any dietary change is to have a sustainable and healthy lifestyle that helps you meet your health goals. Whether you’re looking to lose weight or prevent disease, intermittent fasting is one eating style that may work for you. The most important thing with any diet is to get all of your essential nutrients, appropriate amounts of food, and enjoy your lifestyle in the long run.
Any diet or eating pattern that helps some people may not have the same effect on everyone. That’s why it’s important to not make any significant dietary changes without consulting your healthcare professional or dietitian.
If you’re looking for help navigating all this, book an appointment with me to see if my service can help you. Book a free discovery call with me.
Harvard Health Publishing. (2017, January). Any benefits to intermittent fasting diets? Retrieved from
Harvard Health Publishing (2018, June 29). Intermittent fasting: Surprising update. Retrieved from https://www.health.harvard.edu/blog/intermittent-fasting-surprising-update-2018062914156
Harvard Health Publishing. (2019, July 31). Not so fast: Pros and cons of the newest diet trend. Retrieved from https://www.health.harvard.edu/heart-health/not-so-fast-pros-and-cons-of-the-newest-diet-trend
Mayo Clinic. (2019, January 9). Fasting diet: Can it improve my heart health? Retrieved from https://www.mayoclinic.org/diseases-conditions/heart-disease/expert-answers/fasting-diet/faq-20058334
Mayo Clinic. (2019, August 14). Mayo Clinic Minute: Inter