Intermittent Fasting Side Effects To Watch Out For
Some fasters find that the diet makes them feel sharper and more alert, but alternately, fasting for long periods can also lead to mental fogginess, disrupted sleep, and decreased alertness, Rumsey says. And, she adds, fasting for extended periods of time takes a large toll on your blood sugar levels, causing you to flip-flop between low blood sugar and a spike when you eat again.
What’s Next In Research
Most calorie-restriction and fasting-diet studies have been in younger people, but researchers are beginning to study older adults. A clinical trial conducted by NIA is testing the 5:2 diet in obese people, age 55 to 70, with insulin resistance. People in the experimental group can eat at will for 5 days, and then for 2 consecutive days are restricted to 500 to 600 calories per day. The experiment is designed to find out how 8 weeks of the 5:2 diet, compared to a regular diet, affects insulin resistance and the brain chemicals that play a role in Alzheimer’s disease.
In the coming years, researchers will continue to explore many unresolved questions. What are the long-term benefits and risks of the various eating patterns? Which diets are feasible as a long-term practice? What specific biological effects on aging and disease are triggered by a particular eating pattern? If a specific way of eating is recommended, at what age is it best to start, and is it safe to continue as you get older?
Scientists are exploring many aspects of calorie restriction and fasting and their effects on people of all ages. Some are conducting clinical studies and trials to learn more. If you are interested in volunteering for this type of research, search ClinicalTrials.gov using keywords such as “intermittent fasting,” “time-restricted feeding,” or “calorie restriction.”
Myth #: Intermittent Fasting Is Bad For Women
There is some evidence that women dont respond as well to fasting as men.
One study found that alternate day fasting actually decreased womens glucose tolerance, or how well they process sugar. Another study on women found that intermittent calorie restriction, which is similar to intermittent fasting, made them hungrier and less likely to continue dieting.
However, theres little evidence that its dangerous, or worse for women than a normal meal schedule.
Other studies haveshownthat alternate day fasting or calorie restriction works extremely well for women. Even in the previous study where women felt hungrier and less happy with alternate day calorie restriction, they still lost slightly more weight than those who stuck to a daily calorie deficit.
If youre a woman, theres almost no scientific evidence that intermittent fasting is bad for you, or not as good as eating more often. That said, like with men, intermittent fasting doesnt possess any particularly special properties for you, so you arent missing much if you dont like it.
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How Does Intermittent Fasting Work
Intermittent fasting may help with weight loss simply because if youre not eating for a lot of the day, chances are you are taking in less calories overall. This can lead to a calorie deficit, which results in weight loss.
Aside from calories, intermittent fasting is also thought to trigger a process called a lipolysis response.
When this happens, it means your body has run out of sugar from food and is breaking down stored fat for energy. This breakdown of stored fat may contribute to weight loss.
Experts think many benefits of intermittent fasting may come from this switch in energy sourcesfrom burning sugar to burning fats. However, more research is needed to understand the exact impact on the body.
Experts Weigh In On Whether To Mix Intermittent Fasting And Exercise
Fans of intermittent fasting say consuming fewers calories by skipping meals helps lose weight and leads to other health benefits.
But what happens to your body when you add exercise to the mix?
Matthew Lees and Eric Williamson, both of the University of Toronto’s Faculty of Kinesiology and Physical Education, have studied the effects of intermittent fasting on muscle health in the general population and older adults. Lees, a postdoctoral researcher, and Williamson a Ph.D. student and registered dietician, conducted the research with Associate Professor Daniel Moore.
“Finding ways to lose weight that are as simple as skipping a meal is very difficult because many people find it hard to manage their hunger while being in a caloric deficit,” Williamson says. “But, if they find that their hunger is well managed with intermittent fasting and they plan to exercise at the same time, then it can be an effective tool for losing fat.”
Lees and Willamson spoke to writer Jelena Damjanovic about the benefits of complementing intermittent fasting with exercise.
What is intermittent fasting?
What does the science say about it?
What’s the appeal of intermittent fasting?
What’s the benefit of combining intermittent fasting and exercise?
Are certain types of exercises better paired with intermittent fasting than others?
Does it matter what time of day you choose to fast?
How does age factor in?
So would you advise against intermittent fasting in older adults?
Do Calories Matter When Fasting Summary
- Fasting studies have shown that reducing the hours we consume food causes weight loss without conscious food intake restrictions.
- Consistent adherence to a fasting routine may reduce the need to count calories.
- You can lose your ability to recognize true hunger due to a poor diet, resulting in an increased need to track your calorie intake.
- Pairing intermittent fasting with a low carb/high-fat diet will give you a weight-loss edge and could reduce your need to track calories.
Recognizing True Hunger Matters
It is worth noting that recognizing true hunger is a skill many of us have lost. The refined foods that makeup so much of the standard American diet get digested and absorbed quickly into the bloodstream. The resulting blood sugar spike is followed by an inevitable crash that brings hunger back sooner than expected.
On top of that, years of eating these low-value foods have left many of us insulin resistant, which means that even if we take in a lot of quick digesting calories, our cells resist the energy, and our cravings for more food never go away.
Bottom Line: If your diet was poor before coming to intermittent fasting, you might find it necessary to remaster the skill of recognizing true hunger. Until then, its a good idea to keep track of how many calories you are consuming.
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Weight Loss Requires A Caloric Deficit Intermittent Fasting Does This Automatically
The reason any weight loss diet works is because it reduces your total calorie intake .
This means youll burn more calories than you consume , leading to weight loss.
Intermittent fasting is no exception to this rule.
Skipping entire meals greatly reduces your calorie intake So much so that you dont really have to worry about calories in the meals you do eat.
Given the average woman might aim for 1600-1800 calories per day to lose weight, thats a whopping 30% of calories saved instantly.
If you skip the morning food, even indulging in two large 750 calorie meals later that day, plus a 300 calorie dessert would keep most on track for weight loss.
Summary: Weight loss requires you to consume fewer calories than you burn. Missing one meal per day by fasting can save around 30% of calories in one go.
Fasting Diet Showed Similar Weight Loss
Despite the differing approaches, both groups showed similar results by the time the trial ended.
“We found that the 8-hour time-restricted eating regimen did not produce greater weight loss than the regimen of daily calorie restriction, with both regimens resulting in similar caloric deficits,” the researchers wrote.
Both groups also saw similar losses of body fat, as well as changes to lean body mass and blood pressure. Volunteers in each group also experienced similar levels of “mild adverse events” like headaches, dizziness and constipation, the researchers found.
“These results indicate that caloric intake restriction explained most of the beneficial effects seen with the time-restrictedeating regimen,” they wrote.
In simple terms, the weight loss the volunteers experienced was more down to them controlling what they ate, rather than when they ate it.
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What Foods Can I Eat And What Do I Have To Avoid
This is a huge perk of intermittent fasting: You technically dont have to alter what you eatyou just have to eat within a certain window of time. On an intermittent fasting diet you dont need to avoid any foods, Gans says. However, one should focus on consuming foods that are high in fiber and healthy fats for satiety, such as quinoa, black beans, spinach, strawberries, avocado, and almonds, and of course other nutrient-dense foods for overall health.
At the same time, its a good idea to limit sugary drinks, processed foods, and simple carbs like white bread, advises Cording. Theyre not providing you with much nourishment, she says. You really want to focus on foods that do you a favor.
That said, plenty of people have paired intermittent fasting with another type of diet, like keto. Again, its not a requirement, but doing intermittent fasting while also altering your diet could help you get results faster.
Determining How Many Calories You Should Eat To Maintain Your Weight
To determine how many calories you should eat while intermittent fasting for weight loss, you need to figure out how many calories you need to eat to maintain your weight. From there, you can subtract your weekly 1,700 calories or calculate what 10 percent fewer calories would amount to for you.
I love this article as well as the calorie calculator that it provides. Use the calculator to determine how many calories you need to eat to maintain your weight. Then, calculate how many calories you need to lose weight.
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Myth #: Intermittent Fasting Will Help You Lose Fat Without A Calorie Deficit
Theoretically, you could lose fat by fasting around 12-24 hours, and then gain muscle when you do eat. Some people have also claimed that intermittent fasting optimizes or balances your hormones in a way that helps you store less fat and build more muscle.
The problem with this idea is that your total calorie intake evens out over the course of a day. If you burn 50 grams of body fat during a 16 hour fast, youll gain it back if you eat enough calories to maintain your body weight during the other 8 hours.
Theres also no evidence that intermittent fasting will change your insulin levels enough to affect your body composition.
In one study, people did lose fat after they switched to one meal per day instead of three meals per day. However, the differences were very small, and they werent exercising or closely monitoring their calorie intake. The study also used BIA to measure their body fat levels, which is notoriously inaccurate.
The bottom line is theres no strong evidence that intermittent fasting will help you lose fat without also eating fewer calories than you burn.
How To Get Started With Intermittent Fasting
There are several types of intermittent fasting you can follow:
- The 16/8 or Leangains Method: Fast for 16 hours per day and eat in the remaining 8-hour window. Most people will skip breakfast and eat from 1pm to 9pm for example.
- The 5:2 Diet: Eat normally for 5 days of the week, but only eat up to 600 calories on the other two days.
- Eat-Stop-Eat or Spontaneous Fasting: Fast for a 12 or 24 hour period multiple times per week. There is no real schedule for this one.
- Alternate Day Fasting: Fast for one day and eat normally the next day. Continue to alternate days of fasting and normal eating.
You can view a more detailed description of each type here.
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What Are The Benefits Of The : 2 Diet
According to Ly, a study in the Clinical Nutrition Journal found the 5:2 diet to be a safe and effective protocol for weight loss. It has generally been accepted by researchers as easy to follow too.
Adding in additional factors for dieters, such as group support, increased adherence and impact, research in PLOS One found.
While there arent many studies specifically on the 5:2 diet, research into intermittent fasting has revealed some great health benefits. These include changes in body composition, fat loss, improved heart health and lowered blood sugar levels.
One study published in the Canadian Family Physician journal found that intermittent fasting could aid weight loss in a similar way to calorie restriction, and it could also help to reduce cholesterol.
Research in the Journal of the Academy of Nutrition and Dietetics that looked into the health benefits of alternate day fasting, which is similar to the 5:2 diet, found it could reduce insulin resistance, asthma and even menopausal hot flushes.
Fasting can increase innate healing mechanisms in the body such as autophagy, which is where your body cleans out old and damaged cells, says Carolyn Nicholas, functional medicine certified health coach and director of Health Coaching app Able . Fasting can also help you to become metabolically flexible, basically switching between burning glucose or ketones for fuel.
Should You Try Intermittent Fasting For Weight Loss
There are many effective ways to lose weight, and intermittent fasting is one but its one of many.
Some people find missing just one meal extremely challenging, so its definitely not for everyone.
Also know that some women report issues with menstruation and even fertility problems from long-term fasting. I recommend joining if you want to join the discussion.
And as always you should consult with your doctor before trying any new diet, especially if you take medication.
However, if you are someone who:
- wants to lose belly fat
- is able to skip meals or at least breakfast without complaint
- wants to spend less on food
- wouldnt mind going to the toilet fewer times in a week
- wants to do a lot less cooking and cleaning
intermittent fasting could be game-changing for you.
About Joe Leech, Dietitian
Joe Leech is a university-qualified dietitian from Australia.
He graduated with a Bachelor’s degree in exercise science, followed by a Master’s degree in Nutrition and Dietetics in 2011.
Learn more about him on the About page.
Joe Leech, Dietitian
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How Safe Is Intermittent Fasting
Research also shows that intermittent fasting is likely a healthy weight loss strategy for most people, but there are important exceptions.
According to Gutschow, intermittent fasting isnt appropriate if you:
- Have any history of eating disorders
- Have blood sugar instability
- Are pregnant or breastfeeding
Gutschow also stressed the importance of talking with your doctor before starting an intermittent fasting plan, especially if you take medications that are affected by foods.
Why 3 Pm Is A Key Time To Start Eating Less Food
Peeke also recommended that I stick to having lunch be my biggest meal of the day. Theres a study that a majority of Americans eat over the course of 15 to 16 hours out of the day, with the majority of their calories coming after 3 p.m. Its a recipe for disaster, she says, referencing a study published in November 2015 in Cell Metabolism.
Peeke suggested that rather than having my banana protein shake as an evening dessert and not eating anything before exercising, I instead drink it first thing in the morning. This way, the carbs from the banana would give me an instant source of energy to fuel my workout and my body would be processing the carbohydrates at an optimal time of the day.
The switch immediately paid dividends. I had way more energy throughout my workout. Because my body was working at a higher intensity, I was burning more calories than I would be even if Id been doing fasted cardio. Peeke recommended that I try to stay under a 12-hour window of restricted eating, but I was able to manage my dinnertime to keep my eating in a 10-hour window. Although my weight drifted up by 2 lb, it was because I was adding muscle mass instead of fat. The additional muscle in my arms and shoulders were noticeable. And as my body fat percentage got lower, I started to see some veins popping out of my biceps, forearms, and calves.
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How Intermittent Fasting Works
Intermittent fasting doesnt promote weight loss only because it creates a calorie deficit. Intermittent fasting also induces a metabolic change. What is the metabolic change I am referring to? Its your body switching over to fat burning from glucose burning. If you fast long enough, your body will run out of glycogen, and start producing ketones from your fat cells to use for energy. This is how you can be in ketosis without being on the keto diet.
Myth #: Intermittent Fasting Is Better Than Snacking Throughout The Day
For a while, almost everyone recommended that you eat small meals throughout the day. Self-styled gurus everywhere claimed that it helped keep your blood sugar and hunger under control, boosted your metabolic rate, and provided more energy for your workouts.
Well, we now know that these ideas are false and the guru pendulum has swung in the other direction: many are now saying that eating many small meals throughout the day is actually bad for you, or at least not as good as eating fewer, larger meals.
There is some evidence that eating more than 3-4 meals per day doesnt keep you as satisfied as limiting intake to a few meals per day. However, if that applies to you, you dont need to be intermittent fasting to eat fewer, larger meals.
On the other hand, you can find studies wherein participants were less satiated on 3 meals per day, and found that increasing meal frequency increased feelings of fullness and made it easier to stick to their diets. And again, you can do this with or without following the intermittent fasting protocol.
You may have also heard that eating small meals will make it harder to lose fat because youre keeping insulin levels higher throughout the day. Well, as you learned a moment ago, however, insulin levels average out over the course of the day, and worrying about small fluctuations is pointless. When you eat a large meal, your insulin levels will stay higher for longer, resulting in almost the same effect as snacking.
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