THE PROS AND CONS OF INTERMITTENT FASTING
By now, you must have heard of intermittent fasting. As the name suggests, it focuses on when you eat, not what you eat.
While these alternating intervals of extreme calorie reduction with periods of normal eating may be touted as the holy grail for weight loss, newer studies call fasting into question.
Intermittent fasting may in fact work for certain people. Proponents of the regimen claim that it helps shed pounds faster than traditional diets. It also reduces the risk of heart disease, type 2 diabetes, and inflammation. However, for some people, intermittent fasting can do more harm than good.
But before you jump on the bandwagon of this newest diet trend, understand that the way your body responds to food is unique to you. There are also several types of intermittent fasting, and it affects men and women differently.
So, why is this dietary approach getting so much attention? Before we break down the pros and cons of intermittent fasting, let us first understand what exactly is this craze in the wellness world.
Intermittent fasting (IF) is a dietary approach that focuses on time-restricted eating. The eating pattern cycles through set periods of eating and fasting.
People fast for various reasons, including religious rituals. The practice has been used for centuries to treat a range of illnesses. In fact, you may already be fasting intermittently to some extent without realizing it.
There are many different styles of intermittent fasting. There are programs where food is eliminated on certain days to those where it is only restricted at certain times of the day. This makes it a more approachable practice than most would think.
The most common approaches to intermittent fasting are time-restricted eating, alternate-day fasting, and the twice-a-week method.
Time-restricted plans separate fasting and eating into two windows. The most common types of time-restricted eating are:
- 16/8: This type of Intermittent fasting involves fasting for 16 hours and eating within an 8-hour window. For instance, if you have dinner at 8 p.m., you would fast until noon the next day.
- 18/6: This type is when you fast for 18 hours and eat within a 6-hour window.
- 14/10: This is when you fast for 14 hours and only eat during the other 10 hours.
- 20/4: This type involves fasting though out the day, barring a 4-hour window period.
Twice a week approach or 5:2 method involves eating a normal, healthy diet for 5 days of the week and restricting calories for 2 days. During fasting days, you can eat no more than 500–800 calories. You can choose which days you fast, as long as there is at least 1 non-fasting day in between.
Alternate-day fasting involves fasting every other day. On fasting days, you limit your calories to 500–800 calories, while on other days you eat a normal diet.
While you’re fasting, you can consume water and calorie-free drinks such as black coffee and tea.
Regardless of the ways to do intermittent fasting, all are based on choosing regular periods to eat and fast. Our bodies break down carbohydrates to use them as energy. When the body does not get the required glucose it needs, it begins utilizing fat cells to turn into glucose for energy.
So, after hours without food, the body exhausts its sugar stores and starts burning fat. This is known as metabolic switching. As the stored fat is broken down, your body produces ketones (or ketone bodies), which serve as an alternative fuel source when glucose is in short supply.
This elevation of ketones in the body is known as ketosis which is also the goal of the ketogenic diet.
Now, if you are eating four meals a day, snacking frequently, and not exercising, your body always has a steady stream of glucose to use and does not burn the fat stores. Intermittent fasting works by prolonging the period between meals so that your body burns through the calories consumed during your last meal and begins burning fat.
As with any diet, there are also good and bad that come with IF. Let’s discuss the pros and cons.
1. Promotes weight loss
As we discussed earlier, fasting fosters ketogenesis, allowing your body to burn stored fat for fuel instead of glucose. It may also help you sustain a caloric deficit leading to weight loss.
In a review of several studies, researchers report that there was a significant decrease in fat mass among subjects who participated in intermittent fasting. Results also showed that intermittent fasting, irrespective of the body mass index (BMI), was efficient in reducing weight.
However, in another study that compared the practice with traditional diets, researchers found that the weight loss benefits were similar. Longer trials are needed for conclusive findings.
2. Reduces Insulin Resistance
Research shows that intermittent fasting can lower insulin levels and even improve insulin sensitivity in prediabetic people. Insulin sensitivity is a term used to describe how sensitive the body is to the effects of insulin, and it varies from one person to another. Low insulin sensitivity (also called insulin resistance), can lead to a variety of health issues, including type 2 diabetes.
It may also help reduce fasting blood glucose by lowering concentrations of leptin (a hormone produced by fat cells to regulate hunger) and increasing adiponectin (a hormone that plays a role in lipid metabolism and glucose regulation).
3. Improves Heart Health
Intermittent fasting may help protect our hearts. Human research has found that it can improve factors that are associated with an increased risk of heart disease. These include increased blood pressure, blood lipids, and cholesterol levels along with inflammatory markers such as cytokines and C-reactive proteins.
The metabolic shifts and reduction in calories may also help reduce your resting heart rate.
4. Supports Brain Health
Apart from the heart, intermittent fasting helps your brain too.
Studies show intermittent fasting increases levels of brain-derived neurotrophic factor (BDNF), low levels of which are linked with cognitive impairment and decline as well as depression. Additionally, it may even aid in the growth of new neurons.
5. Decreases Inflammation
Researchers have found that intermittent fasting may effectively combat low-grade inflammation.
While inflammation is a process used by the body to fight off harmful pathogens or recover from injuries by triggering our immune system, long-term (or chronic inflammation) can do more harm than good. Chronic inflammation is at the root of nearly every modern illness, including obesity, diabetes, heart disease, autoimmune disease, Alzheimer’s, and cancer.
Intermittent fasting has been shown to reduce concentrations of inflammation-promoting markers such as interleukin 6, homocysteine, and C-reactive protein which play a role in the development of these chronic diseases.
6. May Increase Your Life Span
Longevity is one of the most widely cited benefits of intermittent fasting. There is accumulating evidence that fasting and calorie restriction could be the fountain of youth.
Eating for 6 hours and fasting for 18 hours can trigger a metabolic switch from glucose-based to ketone-based energy. This can not only increase longevity, but can also enhance stress resistance, and decrease the incidence of diseases, including obesity and cancer.
Animal studies have shown that a 10-40% calorie reduction can result in longer lifespans with less incidence of disease. But just because something works in animals does not mean it will hold for humans. There has been observational research linking religious fasting to long-term longevity benefits, but more human trials are needed.
7. May Play a Role in Cancer Treatment and Prevention
Periodic fasting may help protect normal cells from the toxic effects of chemotherapy drugs while sensitizing cancer cells to the treatment, according to the findings of animal studies. However, the benefits are still inconclusive for humans.
We can still attribute the reduction of the development of cancer to weight control and reduced inflammation brought on by intermittent fasting.
8. Easy To Follow
All you need for intermittent fasting is a watch or a calendar to know when to eat. And unlike many diets that focus on limiting particular foods or focusing on others, with this methodyou simply eat according to the day of the week or time of the day.
9. Unrestricted Eating Allowed
Time-limited intermittent fasting gives you the freedom from having to measure your portions or tabulate daily counts either manually or on a smartphone app. Even the other types of intermittent fasting are simple, where little or no calorie counting is required. There are also no restrictions or targets on specific macronutrients such as carbohydrates.
However, the food restriction during certain hours does not mean you can feast on whatever you want. Continuing to eat unhealthy foods may not be the healthiest way to benefit from intermittent fasting.
10. Could Have Other Health Benefits
Intermittent fasting is not just about weight loss. It can increase your physical endurance, thinking, memory, and even autophagy - an important detoxification function in the body to clean out damaged cells. It gives the body a chance to heal and get rid of junk inside the cells which can accelerate aging.
Some people even report being able to sleep better as a result of intermittent fasting. This could be due to the regulation of circadian rhythm, which determines sleep patterns.
1. Severe Hunger
Your appetite hormones and hunger center in your brain go into overdrive when you are deprived of food. This may become even more extreme when others around you are consuming snacks or typical meals.
2. Side Effects
Some people may experience side effects from intermittent fasting. This is particularly the case when starting the process for the first time. As the body adjusts to calorie restriction, you may experience a fasting headache.
Other potential reactions may include digestive issues such as bloating, heartburn, constipation, nausea, and diarrhea. Dehydration, irritability, dizziness, anemia, and malnutrition are other side effects that may occur.
3. Lower Physical Activity
Those following intermittent fasting may also experience fatigue. This may lead to changes in their regular exercise routine or failure to meet daily steps goals. Moreover, most intermittent fasting programs do not include a recommendation for physical activity.
Your body will need some time to adjust. Try choosing a period or day of the week that you don’t need to be very active when first starting a fasting practice.
Some medications specifically carry the recommendation to be taken with food. In that case, taking medications during fasting may be a challenge.
Speak to your healthcare provider before starting an intermittent fasting protocol if you suffer from any form of chronic illness that requires you to take prescription medications daily. They will check if fasting will interfere with the effectiveness or side effects of your medication.
5. Long-term Limitations
Researchers have found a very high dropout rate among people assigned to the fasting regimen. For instance, a 2017 study published in the JAMA Internal Medicine found that almost 40 percent of people fall off the fasting wagon within 6 months.
This may also reflect a real-life pitfall of fasting as a weight-loss approach. It is only human to want to reward themselves after doing very hard work, such as fasting for a long time.
6. May Still Cause Weight Gain
Yes, intermittent fasting does reduce your overall caloric intake. But if you overindulge during your eating window, you can still gain weight.
This means if you are eating more calories than what your body burns, those pounds are going to pile back up. Fasting does not replace calorie control or healthy eating.
Remember that intermittent fasting is not a free pass to eat piles of fast food and other junk when not fasting.
7. May Influence Disordered Eating
In some people, the restrictive nature of intermittent fasting may trigger unhealthy eating patterns. For instance, if you feel deprived after a day of complete fasting, it may lead to binging behaviors when not fasting.
Make sure you are being honest with yourself before trying any kind of fasting practice. Incorporate basic nutrition principles including a balanced diet and calorie control to set yourself up for success.
Biologically dictated gender roles have played a part in shaping male and female metabolic responses to several things including fasting.
A 2005 study found that women had a slightly worse glucose response than men, after three weeks of intermittent fasting. The men, however, had worse insulin responses.
In a 2006 study, men and women who fasted for 24 hours had slightly different experiences in their self-reported hunger. The women reported feeling hungrier than men in the study.
There are also possible risks for women to consider around bone health, reproductive health, and overall well-being.
Some animal studies even suggest that intermittent fasting may cause changes in estrogen levels and negatively impacts reproductive functions, such as fertility, menstrual regularity, pregnancy, and lactation. However, currently, it is not clear if human females are affected in the same way.
People with certain health conditions will need to be cautious.
Those on medications that need to be taken with food should refrain from intermittent fasting, as cutting out meals could make this impossible.
People with diabetes are at risk of hypoglycemia during fasting, and when combined with anti-diabetic medication, may cause blood sugar to reach dangerously low levels.
Fasting has been linked to an increased risk of bulimia and binge eating, so it is not recommended for people with a history of eating disorders.
Pregnant and breastfeeding women should avoid intermittent fasting. Although there are no specific studies on the effects of fasting during these periods, women generally need more calories and should not go on restrictive diets.
Older adults can be prone to falls and fractures due to fluctuations in energy intake and glucose concentration caused by intermittent fasting.
Intermittent fasting promises weight loss, better health, and longer life and is easy to follow. However, it also has some downsides such as side effects and sustainability issues. It is important to remember that intermittent fasting is not for anyone, and some people may benefit from avoiding it. Speak to your health provider before starting any fasting regimen.
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- Patterson, Ruth E et al. “Intermittent Fasting and Human Metabolic Health.” Journal of the Academy of Nutrition and Dietetics vol. 115,8 (2015): 1203-12. doi:10.1016/j.jand.2015.02.018
- Heilbronn, Leonie K et al. “Glucose tolerance and skeletal muscle gene expression in response to alternate day fasting.” Obesity research vol. 13,3 (2005): 574-81. doi:10.1038/oby.2005.61
- Uher, Rudolf et al. “Cerebral processing of food-related stimuli: effects of fasting and gender.” Behavioural brain research vol. 169,1 (2006): 111-9. doi:10.1016/j.bbr.2005.12.008
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- Heilbronn, Leonie K et al. “Alternate-day fasting in nonobese subjects: effects on body weight, body composition, and energy metabolism.” The American journal of clinical nutrition vol. 81,1 (2005): 69-73. doi:10.1093/ajcn/81.1.69
- Ganesan, Kavitha et al. “Intermittent Fasting: The Choice for a Healthier Lifestyle.” Cureus vol. 10,7 e2947. 9 Jul. 2018, doi:10.7759/cureus.2947
- Malinowski, Bartosz et al. “Intermittent Fasting in Cardiovascular Disorders-An Overview.” Nutrients vol. 11,3 673. 20 Mar. 2019, doi:10.3390/nu11030673
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- Anton, Stephen D et al. “Flipping the Metabolic Switch: Understanding and Applying the Health Benefits of Fasting.” Obesity (Silver Spring, Md.) vol. 26,2 (2018): 254-268. doi:10.1002/oby.22065
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