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Intermittent fasting: Facts vs myths

Intermittent fasting: Facts vs myths

Intermittent fasting is a term used to describe a variety of eating patterns that have alternating periods of fasting — abstinence from foods — and eating.

The fasting period may last from 12 hours per day to several consecutive days, with a consistent, recurring pattern over the course of a week.

The main types of intermittent fasting are:

  • modified fasting or the 5:2 diet — this protocol involves fasting for 2 non-consecutive days of the week, and eating normally for 5 days
  • alternate-day fasting — fasting days are alternated with days where foods and beverages are consumed normally, without restrictions
  • time-restricted eating — a type of intermittent fasting that limits the “eating window” to 4–12 hours, inducing a daily fasting period of 12–20 hours. Persons eat to satiety during their eating windows without caloric restrictions.

Of these, time-restricted eating is the most popular, and may be what most people refer to when they mention intermittent fasting.

The 16:8 pattern — eating during an 8-hour window and fasting for 16 hours each day — may be the most recommended time-restricted eating pattern.

Much of the research on intermittent fasting and time-restricted eating considers the impact of fasting on the body’s natural circadian rhythm.

The circadian rhythm, also called the circadian clock, represents the 24-hour cycle of metabolism in the body, including control of the sleep-wake cycle, blood pressure, mood regulation, and hormonal balance, to name a few.

It is influenced by light and darkness over the course of the day, eating behaviors, and the timing of meals.

A growing body of research suggests that eating for lengthy periods in the day, ranging from 12–15 hours, may disrupt the circadian rhythm and increase the risk of chronic diseases including heart disease, cancer, and type 2 diabetes.

Thus, a major goal of fasting, specifically time-restricted eating, is to reduce the time spent eating in the day by extending the overnight fasting period.

The study of the relationship between circadian rhythms and food timing is called chrono-nutrition.

Many of the benefits of intermittent fasting are attributed to daily fasting periods of no less than 12 hours, although some research suggests that a minimum of 16 hours of fasting may be required.

Generally, during 12–36 hours of uninterrupted fasting, the liver glycogen stores become depleted, overall metabolic processes are altered, and positive health effects are observed.

Here are some of the science-backed benefits of intermittent fasting.

1. Improved cholesterol levels

Findings across animal and human research show favorable changes in cholesterol levels.

Intermittent fasting has the potential to reduce total cholesterol, triglycerides, LDL cholesterol or “bad” cholesterol, and increase HDL cholesterol or “good” cholesterol.

Elevated total cholesterol, LDL cholesterol, and triglyceride levels are risk factors for heart disease.

2. Blood sugar control

Intermittent fasting can improve blood sugar control by reducing insulin resistance, and increasing insulin sensitivity.

This results in lower fasting blood sugar and glycated hemoglobin — HbA1c — levels.

In fact, experimental research in adult males with type 2 diabetes showed the potential for intermittent fasting as a therapeutic approach that may reduce the need for insulin therapy.

3. Changes in body composition

Changes in body weight and composition are among the most studied effects of intermittent fasting.

Several studies have shown that weight loss of between 3–7{cfdf3f5372635aeb15fd3e2aecc7cb5d7150695e02bd72e0a44f1581164ad809} body weight in an average of 8 weeks was achievable through intermittent fasting. Research also noted that this method could result in fat loss.

Fasting in a 14:10 pattern — an eating window of 10 hours and a daily fast of 14 hours — can act on the risk factors of metabolic syndrome, including by reducing waist circumference, body fat percentage, and visceral fat.

Intermittent fasting can thus ease metabolic syndrome, a set of risk factors that increase the risk of heart disease and type 2 diabetes.

4.

A 2015 review of 2,650 adult females indicated that reducing calorie intake in the evenings, and fasting for longer periods at night, may lower inflammation and the risk of breast cancer and other inflammatory conditions.

Observational research of 26,092 adult males over a 16-year period suggested that r.

Other areas of health that intermittent fasting is being explored in include longevity and neurodegenerative conditions like Parkinson’s disease.

Despite the many touted benefits of intermittent fasting, there are also some downsides.

Side effects

Intermittent fasting may be safe for heart and metabolic health, but according to a 2017 review, it may induce negative side effects in some people, such as:

  • increased feelings of hunger
  • heightened irritability
  • worsened mood
  • increased thoughts about food
  • fatigue
  • fears of feeling out of control around food
  • overeating during eating windows
  • difficulty concentrating.

Quality of evidence

Additionally, most of the research on intermittent fasting is based on animal research, with little long-term human research available.

Furthermore, a 2021 review found that only six out of 104 alleged health benefits of intermittent fasting were supported by moderate- to high-quality evidence, and most findings were based on low-quality research.

This means that more rigorous human research on the long-term health benefits of intermittent fasting is warranted.

Intermittent fasting is not the only type of diet to result in the aforementioned benefits.

Calorie restriction

Calorie restriction involving a reduction of about 25{cfdf3f5372635aeb15fd3e2aecc7cb5d7150695e02bd72e0a44f1581164ad809} of daily energy needs without a change in mealtimes had a positive effect on promoting overall health.

Some research suggests that the health outcomes of intermittent fasting are no greater than those observed in calorie restriction diets.

In fact, outcomes for weight and/ or fat loss, body fat percentage, and metabolic risk factors are comparable between the two.

However, research on intermittent fasting shows a greater adherence over longer periods compared to calorie restriction, and suggests that it may be a more sustainable approach.

Mediterranean diet

The Mediterranean diet is a renowned dietary pattern based on the traditional eating patterns of the Mediterranean basin.

Like the potential heart-friendly benefits of intermittent fasting, research shows that long-term adherence to the Mediterranean diet reduces the occurrence of heart attack and stroke by up to 30{cfdf3f5372635aeb15fd3e2aecc7cb5d7150695e02bd72e0a44f1581164ad809} after approximately 5 years.

Additional research on the Mediterranean diet demonstrates its protective nature against the development of colorectal cancer and the loss of nerve cells in Parkinson’s disease.

A major benefit of the Mediterranean diet compared to intermittent fasting is that similar results can be achieved without the need for fasting.

Intermittent fasting describes a variety of eating patterns that alternate periods of fasting and eating with a consistent, recurring pattern over the course of a week.

Time-restricted eating is the most popular form of intermittent fasting and uses the principles of chrono-nutrition to lengthen night-time fasting and potentially reduce chronic disease risk.

Intermittent fasting may improve cholesterol levels, blood sugar control, weight and/ or fat loss, lower inflammation, promote longevity, and support neurodegenerative conditions like Parkinson’s disease.

However, most of the research on intermittent fasting is based on animal studies and human research is sparse and often of low quality.

Alternative non-fasting diets that produce similar results to intermittent fasting include calorie restriction and the Mediterranean diet.

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Facts and myths about its health benefits

Omega-3 fatty acids are a type of polyunsaturated fat — also referred to as “healthy fats” — praised for their potential protective roles in several chronic diseases, such as heart disease and dementia.

They are one of the key building blocks for cell membranes and remain a subject of interest in the scientific community.

The family of omega-3 fatty acids includes:

  • alpha-linolenic acid (ALA)
  • stearidonic acid (SDA)
  • eicosapentaenoic acid (EPA)
  • docosapentaenoic acid (DPA)
  • docosahexaenoic acid (DHA)

DHA and EPA are the primary polyunsaturated fats in brain cell membranes and have been popularized and successfully marketed as dietary supplements.

Omega-3 fatty acids are essential, meaning the human body is incapable of creating them on its own — the fatty acids or their precursors must be obtained from the diet.

For instance, ALA from plant seeds can be converted in the body to all the other types of omega-3 fats: EPA, SDA, DHA, DPA.

However, this conversion is quite inefficient, with rates of less than 3{cfdf3f5372635aeb15fd3e2aecc7cb5d7150695e02bd72e0a44f1581164ad809} of ALA being converted to DHA or EPA in males and less than 10{cfdf3f5372635aeb15fd3e2aecc7cb5d7150695e02bd72e0a44f1581164ad809} in females — warranting adequate dietary intakes of DHA and EPA themselves.

DHA, EPA, and DPA omega-3 fatty acids are synthesized by marine organisms such as algae and phytoplankton.

When consumed by fish, aquatic mammals, and crustaceans, the fatty acids enter the food chain and are stored in body fat, liver, and blubber. They are then later consumed by humans.

Food sources of DHA, EPA, and DPA include:

  • fatty fish, such as salmon, sardines, mackerel, menhaden, or herring
  • the liver of lean, white fish, such as halibut or cod
  • blubber from seals or whales
  • fish oils from cod flesh, tuna, haddock, flounder, or krill oil

ALA, on the other hand, is concentrated in plant sources and is the most frequent omega-3 fatty acid used by the body to create all other types of omega-3 fatty acids.

Sources of ALA include nuts and seeds, such as flaxseed, chia seeds, and walnuts as well as oils, such as echium seed oil, canola, and soybean oils.

According to the National Institutes of Health (NIH), most adults in the United States consume the recommended amount of omega-3 — 1.1 grams (g) for adult females and 1.6 g for adult males — in the form of ALA.

However, given that the conversion of ALA to DHA and EPA is poor, dietary intake of a combination of foods rich in ALA, EPA, and DHA is recommended.

Furthermore, a myriad of DHA and EPA omega-3 supplements are available and contribute significantly to daily omega-3 intake. Fish oil is the most common omega-3 supplement used by adults and children.

Decades of research on the health impacts of omega-3 fatty acids have provided controversial findings. Here are some evidence-backed benefits of consuming omega-3 fatty acids.

Anti-inflammatory properties

Chronic inflammation — also called low-grade inflammation — is linked to the development of obesity, heart disease, and cancers.

Omega-3 fatty acids have been shown to exert anti-inflammatory effects in the human body and may aid in lowering markers of inflammation, such as C-reactive protein and interleukin-6.

In fact, omega-3 fatty acids are regarded as one of the most potent lipids capable of reducing oxidative stress and inflammation. It also potentially guards against the development of chronic diseases.

Lower cholesterol

In a 6-week study, daily supplementation with at least 1.2 g of DHA significantly reduced triglyceride levels and increased “good” cholesterol, or high-density lipoprotein.

In addition, omega-3 fatty acids lowered the “bad” cholesterol, low-density lipoproteins (LDL), when dietary saturated fats were replaced with polyunsaturated and monounsaturated fatty acids found in plants foods such as nuts and avocados.

Elevated triglycerides and LDL cholesterol are linked to an increased risk for metabolic syndrome and heart disease.

However, a recent evidence-based practice summary has shown no impact on a range of cardiovascular disease (CVD) outcomes from the use of omega-3 fatty acid supplements in patients with established CVD or raised risk factors for CVD.

Lower blood pressure

On the other hand, omega-3 fatty acids have been shown to improve vascular health — the health of the blood vessels — by increasing the bioavailability of nitric oxide.

In a phase 2 scientific study, nitric oxide induced dilation (relaxation) of the blood vessels and led to a significant reduction in blood pressure.

May reduce the risk of heart disease

By reducing markers associated with an increased risk of developing heart disease — high triglycerides, cholesterol, and blood pressure — omega-3 fatty acids may reduce the risk of heart disease, according to a review analyzing existing studies.

The same review concluded that high-dose daily supplementation with 4 g of purified EPA in people with elevated triglycerides levels led to a 25{cfdf3f5372635aeb15fd3e2aecc7cb5d7150695e02bd72e0a44f1581164ad809} reduction in cardiovascular events.

In their 2018 review, Prof. Fereidoon Shahidi, professor of biochemistry at Memorial University, Canada, and Prof. Priyatharini Ambigaipalan, currently at the School of Science and Engineering Technology at Durham College, also in Canada, identified evidence of health benefits from omega-3 in noncardiovascular health conditions.

Improve tolerance to cancer treatment

Omega-3 fatty acids may improve the efficacy and tolerance of chemotherapy and is a potential supportive treatment to people undergoing cancer treatment.

More specifically, daily supplementation with EPA and DHA helped patients with head and neck cancers and breast cancer to maintain body weight and reduce cancer-related muscle loss.

Improves depression

A 2019 review study of over 2,000 participants showed a beneficial impact of EPA omega-3 fatty acids on depression, with DHA showing little benefits.

This finding is supported by other studies included in Prof. Shahidi’s and Prof. Ambigaipalan’s review, indicating that fish oil supplementation helps protect against major depressive disorder in people between the ages of 15 and 25 years.

Furthermore, moderate intakes of fatty fish and seafood were associated with fewer occurrences of depression.

Omega-3 fatty acids have been successfully marketed as heart-friendly and reported to reduce the risk of adverse heart disease-related outcomes.

However, its role and health benefits for some conditions have been challenged and discredited. This Cochrane report review found no evidence of the benefit of omega-3 supplements on heart disease, stroke, or death.

Here are some conditions that omega-3 fatty acids may not prevent or improve, based on the latest scientific evidence.

Reduce risk of death by heart disease

Prof. Shahidi and Prof. Ambigaipalan also found that the consumption of omega-3 fatty acids does not reduce the risk of adverse heart disease-related outcomes, such as sudden cardiac death, heart attack, or stroke, even in individuals without a history of disease.

Although omega-3 fats lower the risk of developing heart disease by lowering triglyceride, the “bad” cholesterol LDL, and blood pressure, a meta-analysis of over 80,000 individuals found that their supplementation neither prevented death from all causes nor heart disease.

Prevent blood clots

Anti-clotting effects of omega-3 fatty acids have been proposed by reducing platelet aggregation. However, this finding has been controversial, and the evidence in this regard is weak — typical doses of omega-3 fats from foods and supplements have a mild effect.

Prevent or treat diabetes

Evidence suggests that increasing omega-3 intake does not prevent or treat diabetes.

It does not affect fasting blood sugar, insulin resistance, or glycosylated hemoglobin in those with type 2 diabetes and metabolic syndrome.

Prevent cancer

Omega-3 fatty acids have been reported to reduce the complications of some cancer patients, and early findings look promising. However, there is no evidence of any action of omega-3s preventing the development of cancers.

In a meta-analysis of over one million people, a particularly high intake of omega-3 fats — 5–15 g per day — did not significantly reduce lung cancer risk, and in some cases, increased the risk of developing lung cancer.

Therefore, too low or too high omega-3 intake may be harmful.

Omega-3 polyunsaturated fatty acids are essential compounds that are key building blocks for cell membranes, particularly in the brain.

For decades, they have been the subject of scientific interest, but findings have been controversial and inconsistent.

The evidence shows that omega-3 fatty acids have anti-inflammatory properties and may lower cholesterol, blood pressure, depressive episodes, weight loss during cancer treatment, and the risk for heart disease.

However, omega-3 intake does not reduce the risk of adverse and severe heart disease-related outcomes, including sudden death and stroke. Additionally, it cannot prevent or treat diabetes or prevent blood clots.

This is an emerging area of evidence, and further results will continue to inform health recommendations.