Irregular Eating Habits Adversely Affect Metabolism

Irregular Eating Habits

In many ways, the human body is like a well-oiled machine. It should run smoothly and with regularity.

However, some unhealthy lifestyle habits, such as poor sleep and irregular eating patterns, may disrupt its natural rhythms.

A recent study compared the effects of regular and irregular eating habits on metabolism — blood sugar control, calorie expenditure and appetite. Below is a detailed summary of its findings.

Irregular Eating Habits


In developed societies, food is always available, and acquiring it doesn’t require hard work or preparation. As a result, most people can chose when they eat and how much.

When food is easy to acquire, people who have difficulty controlling their food intake tend to overeat and gain weight. They also snack more often and eat irregularly.

For this reason, some observational studies have associated irregular eating patterns with an increased risk of obesity and metabolic disease (1, 2, 3).

However, growing evidence from controlled studies suggests that irregular eating patterns may affect metabolism irrespective of calorie content. For example, eating irregularly may:

  • Reduce the thermic effect of food
  • Lower fasting insulin sensitivity
  • Increase insulin levels after a test meal
  • Raise levels of total cholesterol and LDL-cholesterol
  • Decrease self-reported calorie intake

These adverse effects of meal irregularity may have something to do with the body’s time keeping system.

Research indicates that irregular eating habits disrupt the body’s clock, which normally helps your body anticipate and prepare for food intake.

Irregular breakfast habits may be one sign of an overall irregular meal pattern.

Most controlled studies suggest that skipping breakfast or eating most of your daily calories late in the day, may promote weight gain and metabolic disease, although not all studies agree (4, 5, 6, 7, 8).

Article Reviewed

This study examined the effects of irregular meal patterns on carb metabolism, the thermic effect of food, blood lipids, gut hormones and appetite.

Irregular meal-pattern effects on energy expenditure, metabolism, and appetite regulation: a randomized controlled trial in healthy normal-weight women.

Study Design

This randomized crossover trial examined how eating irregularly affects metabolism, compared to eating regularly.

The researchers recruited 11 lean and healthy 18–40 year old women.

They were assigned to two 14-day treatment periods in a random order:

  • Regular meal pattern: For 2 weeks the participants followed a regular meal pattern consisting of 6 meals per day.
  • Irregular meal pattern: For 2 weeks the participants followed an irregular meal pattern consisting of 3–9 meals per day.

The study had a crossover design, which means that all participants were assigned to both treatments in a random order, separated by a 14-day washout period.

During both treatment periods, the participants were asked to consume meals at specific times of the day between 8 AM and 9 PM to ensure either the regularity or irregularity of the meal pattern.

They also followed a standardized weight-maintenance diet, providing roughly 50% of total calories from carbs, 35% from fat and 15% from protein.

Before and after each treatment period, the researchers measured calorie expenditure and took blood samples.

All blood samples were taken in the morning after a 12-hour overnight fast and again several times following a test drink.

Circulating levels of blood sugar, blood lipids, insulin, glucagon-like peptide 1 (GLP-1), peptide YY (PYY) and ghrelin were measured in blood samples, and insulin sensitivity was calculated.

Blood sugar was also continuously monitored for 3 successive days during each treatment period.

Additionally, the participants were asked to rate their appetite on a visual analog scale (VAS) before and after a pasta-based test meal on days 7 and 14 of each treatment period.

Bottom Line: This was a randomized crossover trial comparing the effects of regular and irregular eating habits on calorie expenditure, blood sugar control, hormones and self-reported appetite.

Finding 1: Eating Irregularly Decreased the Thermic Effect of Food

After you eat there’s a temporary increase in the amount of calories you burn. This rise in calorie expenditure is known as the thermic effect of food (TEF) or diet-induced thermogenesis.

The study showed that TEF increased significantly during the regular meal pattern intervention.

Specifically, the rise in TEF was considerably higher following a regular meal pattern, compared to the irregular meal pattern, as seen below.

Thermic Effect of Food

These findings are supported by previous studies showing that meal irregularity leads to decreases in the TEF ( 4, 5).

In contrast, there were no differences in average, free-living calorie expenditure or resting calorie expenditure.

Bottom Line: Eating irregularly reduced the thermic effect of food, an effect that might promote weight gain in the long-term.

Finding 2: Eating Irregularly Increased Hunger

Mean hunger ratings after the test drink decreased by 195% during the regular meal pattern intervention but only by 104% following the irregular meal pattern.

Hunger ratings were also significantly higher before and after the test meal on day 14 (the final day) of the irregular meal intervention, compared to the regular meal intervention. These findings are shown in the chart below.


Despite these increases in hunger, calorie intake during the test meal remained unchanged.

Since the participants were on a weight-maintenance diet and the study period was short, the researchers observed no significant changes in body weight.

Bottom Line: Eating irregularly increased subjective ratings of hunger. However, these changes in appetite did not significantly increase calorie intake at a test meal.

Finding 3: Eating Irregularly Reduced Levels of PYY After a Meal

Peptide YY (PYY) is a hormone that reduces appetite. Its levels increase after you eat and decrease during fasting.

This study showed that the mean levels of PYY decreased after both treatments. However, this decrease was greater after eating irregularly for 2 weeks.

Specifically, eating irregularly decreased the levels of PYY by 23%, whereas eating regularly decreased its levels by 9%.

Given that PYY may reduce appetite, the irregular eating pattern should have increased appetite or hunger. This is consistent with the results for self-reported appetite.

Bottom Line: Eating irregularly decreased mean levels of PYY, which is an appetite reducing hormone.

Finding 4: Irregular Meals Impaired Blood Sugar Control

This study showed that blood sugar levels were higher after breakfast on days 7 and 9 of the irregular eating intervention than during the regular eating intervention.

Additionally, blood sugar levels were significantly higher after the test drink on day 14 of the irregular meal pattern, compared to the regular meal pattern, as seen in the chart below.

irregular eating

No other significant differences in blood sugar levels or insulin were detected.

These findings are consistent with other studies showing that irregular eating habits may impair blood sugar control (9).

Bottom Line: Eating irregularly for 2 weeks slightly reduced blood sugar control.


This well-designed study didn’t seem to have many faults.

However, the study was relatively short. Further studies are needed to examine the long-term effects of irregular eating patterns.

Additionally, the study only recruited lean women. The findings don’t necessarily apply to men or obese individuals.

Summary and Real-Life Application

This study showed that eating irregularly may increase hunger, impair blood sugar control and reduce calorie expenditure after meals.

Taken together, these changes suggest that irregular eating may lead to weight gain and metabolic imbalances over time. However, the study was too short to detect any significant changes in body weight.

Simply put, eating regularly at specific times of the day (without overeating) and avoiding snacking between meals is probably good for your health and waistline.

Written by Aline Pilani

Hey, I’m Aline Pilani. I am a certified personal trainer and nutritionist. I have spent the last 10 years of my life helping people losing weight, increase their health and confidence, and I truly want to do the same for you.