Updated: Sep 21
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. 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 a longer life.
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—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—not better—than 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. Other people who intermittently fast struggle with and are much more uncomfortable during the fasting days, and some animal studies show that when they were allowed to eat as much as they wanted, many overate.
What about extending the lifespan of humans? Those studies haven’t been done yet, so we simply don’t know the effects of intermittent fasting on our lifespan.
How intermittent fasting affects 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.
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 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 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. 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.
On a molecular 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.
More research is underway to better understand the effect of fasting on these biological processes.
Before you start intermittently fasting
As with all major dietary changes, be sure to discuss it with your healthcare professional [or book a consultation with one of our fabulous RDNs! https://www.buffalo-nutrition-and-dietetics.com/scheduling].
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.
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 is simply 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.
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, vegetables, legumes, and whole grains. Also, avoid too many sugars and refined grains. An RDN can provide recipes and meal plans that incorporate your preferences while taking into consideration that fasting days often limit calorie intake to ~500-600/day.
Feeling Empowered? 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.
If you’re looking for assistance, book an appointment with us - we are delighted to guide you on your path to success.
This article is dedicated to my father in law, Rob, who has not only been a long time advocate for fasting, but has had incredible success in doing so. As a retired engineer with the curiosity of those who further science, I can always rely on him to "nerd out" with on the latest medical nutrition research.
~Tricia Sauer, RDN, CDN, IFNCP
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