by Julie Pace, RDN | Jan 11, 2021
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, Mediterranean, MIND, etc. With so many choices, how do you know which one is right for you?
What is 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.
Most 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.
Here are a few different approaches to intermittent fasting:
- 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 number 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.
It is important to note that going for long periods of time 24, 48, 72 hours of fasting periods are not necessarily better for you and may actually be very dangerous. In addition, going for too long without eating may encourage the body to start storing more fat in response in starvation.
Benefits of intermittent fasting
Studies show that intermittent fasting can promote weight loss. However, when it comes to weight loss, intermittent fasting seems to work just as well—not better—than other diets.
Research suggest eating this way suppresses 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. Other people who try intermittent fasting struggle with hunger and are much more uncomfortable during the fasting days. As a result, those who struggle with hunger during fasting may overeat during periods of eating.
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 increase exercise endurance, support immune function, and increase longevity. Intermittent fasting may also support the body’s ability to help resist some diseases like diabetes, heart disease, certain cancers, and Alzheimer’s.
When it comes to clinical studies on intermittent fasting, most have been pretty short—a few months or less. What we know so far is that it may help reduce markers of inflammation like C-reactive protein, diabetes, blood glucose levels, insulin sensitivity, and help to reduce high blood pressure and cholesterol.
Other research supports the beneficial effect that intermittent fasting has on sleep cycles and the gut microbiome. Fasting gives the gut microbes a period of rest time and improves and maintains the population of good bacteria.
Overall, research on the effect of intermittent fasting on people’s health is still emerging as to whether it is beneficial for weight loss and disease prevention.
How does intermittent fasting affect overall health?
Naturally, our bodies have survival mechanisms allowing us to adjust to periods of fasting. This has been necessary, as throughout history, humans have endured many periods where food was scarce.
What happens when we don’t take in sufficient calories is that 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.
This is when your metabolism shifts from a carbohydrate-burning state to a fat-burning 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. They 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 disease like Alzheimer’s.
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 the other hand, too many ketones may be harmful, so more research is needed to better understand the links between fasting, ketones, and health.
Before you start intermittent fasting
Before considering intermittent fasting, you should understand that there are certain health conditions that can make it dangerous. For example, if you have diabetes you need to eat regularly to maintain your blood sugar levels, therefore, 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.
Some people who restrict their calories or start intermittent fasting may experience side effects which includes 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 is simply hard to do voluntarily—especially when it’s for two or more days. As a result, some people may have a natural tendency to indulge too much on their “feast” days which can negate some of the benefits of 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.”
As with all major dietary changes, be sure to discuss it with a registered dietitian nutritionist or your healthcare professional before making significant changes to your diet. `
Intermittent fasting can be hard. If you choose to try IF, one suggestion that may be helpful is having a social support network—especially for those days when you’re fasting, Even though the idea of intermittent fasting is to restrict when you eat, not what you eat, the quality of your food choices matters because you still need your essential nutrients.
To sum it up
The main goal in dietary changes should be to create sustainable nutrition and healthy lifestyle habits that will help you meet your health goals and promote optimal wellness. Whether you’re looking to lose weight or prevent disease, support immunity, or improve your gut health, I recommend choosing a pattern of eating that is enjoyable, sustainable and practical for you.
It’s important to remember that one particular diet or eating pattern that helps some people may not have the same effect on everyone. Considering all the different diets that there are to choose from, you may find it frustrating trying to figure out which one will work best for you.
If you need some guidance in deciding which eating pattern will be most practical for you, schedule a free discovery call with me to see how my programs can help you optimize you health and reach your health goals.
References:
Harvard Health Publishing. (2017, January). Any benefits to intermittent fasting diets? Retrieved from
https://www.health.harvard.edu/diet-and-weight-loss/any-benefits-to-intermittent-fasting-diets
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
https://www.nia.nih.gov/health/calorie-restriction-and-fasting-diets-what-do-we-know
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
https://www.nih.gov/news-events/nih-research-matters/intermittent-dietary-restriction-may-boost-physical-endurance
National Institutes of Health NIH Research Matters (2018, September 18). Fasting increases health and lifespan in male mice. Retrieved from
https://www.nih.gov/news-events/nih-research-matters/fasting-increases-health-lifespan-male-mice
NIH Intramural research program. (2018, March 13). Intermittent Fasting Boosts Endurance in Mouse Marathoners. Retrieved from
https://irp.nih.gov/blog/post/2018/03/intermittent-fasting-boosts-endurance-in-mouse-marathoners
NIH National Center for Advancing Translational Sciences. (2018, August). NCATS-Supported Study Shows Eating Before 3 p.m. Can Improve Health. Retrieved from
https://ncats.nih.gov/pubs/features/ctsa-kl2-fasting
