Of intermittent fasting

(T2DM). There is evidence of an effect of the IF diet on the activity of pancreatic B-cells in patients with T1DM.

Effects of IF on energy intake

The main reason why individuals lose weight with IF is because these interventions help people to reduce energy intake. Studies indicate that ADF, the 5:2 diet and TRE reduce overall energy intake by approximately 10–30 per cent relative to baseline.

Clinicians are often worried that patients on ADF or the 5:2 diet will overeat on feast days. However, accumulating evidence suggests that this does not occur. Participants typically only consume an extra 10–15 per cent of their energy needs (approximately 200–300 kcal) on feast days relative to their calculated energy needs.

Indeed, one study found reduced energy intake on feast days in individuals on the 5:2 diet compared with energy intake before the start of the study.

As participants do not fully compensate for lack of food consumed on the fast day by eating more on the feast day, a net energy deficit is created, resulting in mild to moderate weight loss.

Effects of IF on diet quality

As IF permits ad libitum food intake on certain days of the week, or during certain time windows in the day, dieticians and physicians have expressed concerns regarding the effects of these eating patterns on diet quality.

These concerns include whether individuals would lower their fruit and vegetable intake and eat more energy-dense and high-fat foods while on IF diets. Changes in macronutrient and beverage intake have been assessed.

Studies have shown that fasting does not seem to have any beneficial or detrimental effects on diet quality.

However, it should be noted that many of these studies advised participants to be mindful of their eating habits during periods of ad libitum intake, which might have confounded the dietary intake data.

IF and metabolic disease risk factors

While the body is abstaining from food, the concentration of glucose, which is the basic energy substrate, decreases. Glycolysis (breakdown of glucose) is inhibited.

Glycogen reserves in the liver are consumed and the process of gluconeogenesis (synthesis of glucose from non-carbohydrate metabolites) is activated, during which fats are consumed.

In addition, insulin and IGF-1 (insulinlike growth factor-1) levels are reduced in blood and glucagon levels rise. Fatty acids released from fat cells in the process of lipolysis (hydrolysis of triglycerides) of triacylglycerol and diacylglycerol are released.

They are then transported to the liver cells, where they are converted into beta-hydroxybutyrate (BHB) and acetoacetate (AcAc) in the beta-oxidation process and are further released into the blood and used as a source of energy for body cells, including the brain.

Such biochemical changes are accompanied by cellular and molecular adaptations of neuronal networks in the brain. The result is an improvement of their functionality and resistance to stress, injuries, and diseases.

The above biochemical transformations of lipids, along with following the IF diet, result in weight loss and changes in lipid parameters.

According to studies conducted by Surabhi Bhutani et al., during the use of alternative days on an empty stomach—ADF (alternate day fasting)—for two–three weeks showed a reduction in body weight by 3 per cent, while longer attempts to use ADF showed a reduction of 8 per cent and reduced fat mass in viscera.

In addition, the levels of total cholesterol (TC) triglycerides and low-density cholesterol (LDL) and the size of these molecules were reduced. Changes in these parameters limit the risk of developing coronary heart disease (CHD).

Cardioprotective effects of the ADF diet are probably associated with a reduction of fat tissue (especially visceral fat tissue), increased adiponectin concentration, and decreased leptin and low-density lipoprotein (LDL) concentration.

While some studies have shown beneficial effects that the use of IF allows body weight to be reduced and is cardio protective, others have shown no benefit.

Effects of IF on blood pressure

The effects of ADF, the 5:2 diet and TRE on blood pressure are highly variable. While several studies have demonstrated reductions in systolic blood pressure (3–11% decrease from baseline) and diastolic blood pressure (3–13 per cent decrease from baseline), several others have shown no effect.

However, it would seem that many of the trials that showed improvements involved participants with elevated blood pressure at baseline. Thus, it is possible that IF might only help to lower blood pressure in people with hypertension or borderline hypertension at the start of treatment.

Based on findings to date, the three forms of IF seem to produce similar reductions in blood pressure, with no apparent deviations between diets.

Effects of IF on plasma levels of lipids

Changes in plasma concentrations of lipids were assessed in trials evaluating IF. Levels of LDL cholesterol decreased by 10–22 per cent from baseline in three trials of IF, but showed no change in the majority of studies.

Triglyceride concentrations also decreased by 16–36 per cent from baseline, but this decrease was not consistent between studies.

When direct comparisons were made between intermittent fasting and calorie restriction, similar decreases in levels of LDL cholesterol and triglycerides were noted, suggesting that these two interventions have equivalent effects on these lipid parameters.

Levels of HDL cholesterol, by contrast, generally remain unchanged or slightly decrease with IF. However, levels of HDL cholesterol typically reduce during periods of acute weight loss. Subsequently, during periods of weight maintenance, HDL cholesterol tends to rebound to baseline levels.

Practical considerations

The positive effect of the IF diet has also been documented in obese and diabetic people. The reduced amount of food consumed when using the IF diet results in a decrease in body weight. It also improves glucose metabolism and increases the sensitivity of tissues to insulin by increasing the B cells of the pancreatic islets.

It remains questionable if these benefits are solely due to weight loss or non-weight loss mechanisms. The success of every type of diet depends on rule compliance — following a prescribed diet according to the circadian rhythm.

Despite the intermittent fasting diet having many benefits, its disadvantages are not without significance. Fasting may be dangerous and it is not recommended for people with hormonal imbalances, pregnant and breastfeeding women, and diabetics.

Moreover, people with eating disorders, a BMI under 18.5, and underweight people are also not recommended to use the intermittent fasting diet.

Who can do IF?

 Adolescents with severe obesity (>95th BMI percentile);

 Adults with normal weight, overweight or obesity;

 Adults with hypertension and/or dyslipidaemia;

 Patients with insulin resistance or prediabetes; and

 Patients with T1DM or T2DM.

Who should not do IF?

 Children under the age of 12 years;

 Adolescents who are normal weight;

 Women who are pregnant or lactating;

 Individuals with a history of an eating disorder;

 Individuals with a BMI below 18.5kg/m2; and

 Individuals over the age of 70 years.

Considerations for diabetes mellitus

Although the evidence is still very limited, preliminary findings suggest that IF might be safe in patients with T1DM and T2DM. However, patients with diabetes mellitus need to be monitored closely by their physician during periods of IF.

Studies show that occurrences of hypoglycaemia (low blood glucose level) and hyperglycaemia (high blood glucose level) are rare in these patients when appropriate medical management is in place.

Conclusion

The health benefits of IF are gradually being clarified as new evidence continues to emerge. Initial studies have shown that dietary practice of using IF has an impact on the bodyweight of overweight or obese individuals.

Findings to date suggest that ADF, the 5:2 diet and TRE produce mild to moderate weight loss (3–8 per cent loss from baseline) over eight–12 weeks. This degree of weight loss is on par with that achieved with traditional dieting approaches (daily calorie restriction).

The impact of IF on cardiometabolic risk parameters is still uncertain. While some studies have demonstrated improvements in blood pressure, LDL cholesterol, triglycerides, insulin resistance and HbA1c, others have shown no benefit on these parameters.

Regarding safety, preliminary data indicate that fasting produces few gastrointestinal, neurological, hormonal or metabolic adverse effects. However, as adverse outcomes are not regularly assessed in human trials of fasting, definitive conclusions regarding the safety of these diets are difficult to draw at present.

Taken together, these initial findings suggest that fasting might be effective for weight loss, but the effects of these diets in the prevention and management of metabolic disorders needs further clarification.

Dr SIVASELVAM SIVAKUMAR

is the head of Lab and Transfusion Services at Oceania Hospitals Pte Ltd. The views expressed are the author’s and do not necessarily reflect the views of this newspaper.