There are so many diets out there to choose from, most of which promise to help people lose weight and reduce their risk of disease: low-fat, low-carb, ketogenic, paleo, whole 30, vegetarian, vegan, DASH, Mediterranean, MIND, etc. I want to talk about one of the latest trends and more importantly, to discuss the science of intermittent fasting. In general, you're probably used to eating three meals a day, as well as snacks. With intermittent fasting, you may eat as much of whatever you want, but you have to stay on schedule. There are scheduled periods of time when you can eat and others when you must fast. In contrast to most other diets, intermittent fasting instructs you when to eat, not what to eat.
Intermittent fasting comes with many promises, and some say that it can lead you to better health and a longer life.
Sound interesting?
Let’s dive into some of the pros and cons of intermittent fasting.
How to intermittently 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) for certain durations of time (intermittently), while allowing little or no restrictions the rest of the time.
Intermittent fasting essentially means skipping meals on a regular basis, sometimes daily, weekly, or monthly. Here are a few different approaches:
Time-restricted feeding: All meals are consumed within an 8-12 hour window each day.
Alternate day fasting: Alternately between regular amounts of calories and minimal calories, day-to-day.
5:2 eating pattern: Five days per week is spent consuming meals regularly, the other two are restricted to 600 calories per day. (This is very little by the way, so you are eating one meal and mostly drinking water.)
Periodic fasting: Calories are restricted for a certain period of time then regular eating is resumed. For example, fasting for five straight days per month.
Benefits of intermittent fasting
Intermittent fasting can achieve weight loss. The success is similar to other diets.
Overall, research on the effect of intermittent fasting on 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.
Much of the research on calorie restriction and intermittent fasting have been conducted in animal research. 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 disease.
Although most clinical studies on intermittent fasting (those done in people) are short, what we know so far is that it might help improve inflammation markers (C-reactive protein), diabetes symptoms (blood glucose and insulin sensitivity), and reduce high blood pressure and cholesterol.
Eating regularly and weight loss seems to be just as (not more) effective when you intermittently fast. Slowing down the body’s metabolism might be one explanation. The less hungry you are, the less you eat, which will assist you in dropping pounds. On the other hand, some individuals who intermittently fast find fasting days more unpleasant and consume more than usual on non-fasting days.
What about extending the lifespan of humans? This is an ongoing area of study and research.
How intermittent fasting affects health
Our bodies have survival mechanisms that allow us to endure periods of fasting. Throughout history, humans have been forced to endure periods of starvation. Apart from this, our bodies have survival mechanisms that allow us to adjust to periods of fasting. When we do not consume enough calories, our bodies start consuming stored carbohydrates called glycogen. Beyond 16 hours, the body switches from using carbohydrates as energy to using fats.
From then on, the body enters into a fat-burning metabolic state. As a result, it switches from a carbohydrate-burning metabolic state to a fat-burning metabolic state. Some of the fat is used directly as fuel, while some is metabolized into biochemicals called ketones. This new fat-burning metabolic state is called ketosis. The state of ketosis brings on other changes throughout the body. It’s these changes that are thought to underlie some of the health benefits seen with intermittent fasting.
Ketones are a more efficient source of energy for our bodies than glucose, and they can help keep many of our cells working well even during periods of fasting. This is particularly true for brain cells. This may be part of the reason some animal studies show protection against age-related declines like Alzheimer’s disease.
Ketones may also help to ward off some cancers and inflammatory diseases like arthritis. They are also thought to reduce the amount of insulin in the blood which may help protect against type 2 diabetes. On balance, too many ketones may be harmful, so more research is needed to better understand the links between fasting, ketones, and health.
On a molecular level, restricting calories may slow down age-related changes and animal studies have shown improved lifespan. We have some control over how our genes are expressed, and intermittent fasting seems to have beneficial effects for certain populations.
More research is underway to better understand the effect of fasting on biological processes.
Before you start intermittently fasting
As with all major dietary changes, be sure to discuss it with your healthcare professional or schedule an appointment with me – so we can discuss if this is right for you.
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, so fasting is not recommended. Also, if you’re taking certain medications like diuretics for high blood pressure or heart disease, intermittent fasting increases your risk for electrolyte abnormalities.
Intermittent fasting is also not recommended for anyone who is under 18, has a history of eating disorders, or anyone who may be pregnant or breastfeeding.
To note, whenever you change the way you eat you may experience side effects. Some side effects of people who restrict their calories or start intermittently fasting include fatigue, weakness, headache, reduced sexual interest, and a reduced ability to maintain body temperature in cold environments.
Beyond the health risks and side effects, fasting can be tough! If you feel like you are punishing yourself, have a serious lack of energy, or are suffering with too many side effects, this is not the diet for you.
Nutrition tips for intermittent fasting
Intermittent fasting can be hard. One thing that can help is having a social support network and an accountability partner, especially for those days when you’re fasting.
Although the premise of intermittent fasting is to restrict when you eat, not what you eat, it is still important to select healthy options. You still need all of your essential nutrients, regardless of your feasting and fasting periods. Intermittent fasting is not a good reason to binge on high-calorie nutrient-poor foods (we all sometimes crave). I recommend consuming adequate amounts of lean proteins, healthy fats, fruits, veggies, legumes, and whole grains. I also recommend avoiding too much sugar, simple carbohydrates, and refined grains.
The Bottom Line
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.
Book an initial consultation appointment with me today to see how you can reach your goals.
References:
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: Intermittent fasting facts. Retrieved from https://newsnetwork.mayoclinic.org/discussion/mayo-clinic-minute-intermittent-fasting-facts/
National Institutes of Health National Institute on Aging. (2018, August 14). Calorie Restriction and Fasting Diets: What Do We Know? Retrieved from
National Institutes of Health NIH Research Matters (2015, July 13). Health Effects of a Diet that Mimics Fasting. Retrieved from https://www.nih.gov/news-events/nih-research-matters/health-effects-diet-mimics-fasting
National Institutes of Health NIH Research Matters. (2017, September 26). Calorie restriction slows age-related epigenetic changes. Retrieved from https://www.nih.gov/news-events/nih-research-matters/calorie-restriction-slows-age-related-epigenetic-changes
National Institutes of Health NIH Research Matters (2018, March 6). Intermittent dietary restriction may boost physical endurance. Retrieved from
National Institutes of Health NIH Research Matters (2018, September 18). Fasting increases health and lifespan in male mice. Retrieved from
NIH Intramural research program. (2018, March 13). Intermittent Fasting Boosts Endurance in Mouse Marathoners. Retrieved from
NIH National Center for Advancing Translational Sciences. (2018, August). NCATS-Supported Study Shows Eating Before 3 p.m. Can Improve Health. Retrieved from
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