The modern world is a fast-paced and rapidly evolving landscape. Many succumb to the rat race of life and feel forced to endure an increasingly hectic schedule in an attempt to get ahead. Combine this with the current food environment, which gives unlimited access to cheap, energy-dense, hyper-palatable foods, and it becomes easy to understand how certain dietary patterns and health consequences have crept to the forefront of society. At present, approximately 42.4% of the population is obese. This has increased from 30.5% in 1999-2000 and is expected to continue rising. By 2030, it is projected that about one in two adults will have obesity.
Due to our on-the-go lifestyle, it may not be surprising to learn that this climb in obesity has coincided with a rise in snacking and less sit down meals. Indeed, when examining the eating trends of American adults over the past 40 years, we see a rise in the relative contribution of energy from snacks alongside a decline in the percentage of 24-hour energy consumed from lunch and dinner.
This widespread trend of increased eating frequency has been documented under close inspection of a small subset of the population as well. For three weeks, the daily temporal pattern of caloric intake was monitored in a cohort of free-living humans via a smartphone app. In the end, some interesting patterns were found which provide more evidence about certain nutritional habits that could be playing a major role in the obesity crisis.
The results showed there were only five hours per day when the number of caloric events was less than 1% of total events and this was between 1-6 a.m. In conjunction with this finding, a traditional breakfast-lunch-dinner feeding pattern was largely absent amongst subjects. The number of caloric events ranged from 3.33 to 10.55 times per day and the median daily eating duration was 14 hours and 45 minutes.
From these data, a clearer picture starts to emerge. In addition to the aforementioned behaviors of increased snacking and decreased sit down meals, it appears our eating patterns lack structure and consistency. We may be routinely eating around the clock, but the timing and frequency of these caloric events fluctuate daily. I would refer to these dietary trends more specifically as rampant “mindless” snacking.
As a result of the modern food environment and our busy lifestyle, it is difficult to resist the frequent call of tasty treats. Many eating occasions are being driven by hedonic desires rather than hunger signals and satiety cues. This has resulted in an increase in snacking and ubiquitous weight gain.
With these trends in mind, let’s perform a more detailed examination of snacking through taking a look at trials that have assessed the effects of snacking on hunger and satiety, as well as energy intake at subsequent meals.
The Pitfalls of Snacking
Over the past several decades, we have grown accustomed to eating more frequently. This pattern has corresponded with an increase in overall energy intake and a subsequent rise in obesity. Other research has linked increased eating frequency and snacking with an increased risk for type 2 diabetes. Unsurprisingly, this finding could be explained by a higher BMI as a result of increased energy intake.
To further examine this link, we can look at the results from more rigorous trials exploring the effect of a snack on subsequent energy consumption. In one such study, they examined the effect of three different snacks varying in macronutrient composition on total energy intake at an ad libitum buffet dinner.
The researchers found that regardless of whether the snack was rich in protein, carbohydrate, or fat, having a snack two hours before dinner did not result in a decreased intake compared to having no snack at all prior to the meal. Otherwise put, the subjects did not reduce their energy intake at dinner to compensate for the snack, leading to higher overall energy intake.
These findings, which allude to the weak satiety effects of snacks, have been replicated elsewhere. In a crossover trial comparing a low-eating frequency of three meals per day to a high-frequency “grazing” meal plan of eight meals per day, subjects reported significantly stronger hunger and desire to eat, as well as less fullness, when consuming the same number of calories over more frequent feedings.
Overall, it appears that a high frequency of eating occasions that contain a relatively small number of calories is a poor strategy for hunger management. Such an eating pattern may ultimately result in eating around the clock, excess energy intake, and weight gain.
Indeed, a review looking at data from both controlled feeding studies and free-living studies has concluded that the totality of the evidence supports snacking, or eating between main meals, especially in a non-hungry state, is detrimental to energy regulation and likely leads to weight gain. This idea is further corroborated by sports and clinical nutrition science.
Due to strenuous training and large levels of muscle mass, athletes often have energy expenditures two to three times the average sedentary individual and as such, require a high daily energy intake. From examining the dietary patterns of athletes, we learn that this population tends to have a “grazing” meal pattern or very frequent feedings. It’s quite common for athletes to utilize at least five and upwards of ten eating occasions per day to meet their energy needs.
The rationale behind this dietary strategy being it is easier to eat a large number of calories per day through smaller more frequent feedings due to these caloric events having less impact on satiety. In fact, a relationship has been found between the number of daily eating occasions and total energy intake in athletes. The more often an athlete eats, the higher their daily calorie intake tends to be.
In regards to the clinical setting, small frequent meals are commonly recommended for patients with conditions that predispose them to inadequate energy intake. For example, small frequent meals are recommended for patients with gastroparesis. Gastroparesis is a disease of the muscles of the stomach resulting in delayed gastric emptying and early satiety. In order to increase energy intake in this population, small frequent meals have been successfully implemented.
Cancer patients are another group who suffer from early satiety and subsequent weight loss. In fact, a primary goal of cancer treatment is to prevent unintended weight loss. For those experiencing early satiety or anorexia, it is recommended to consume small frequent meals.
The benefits and efficacy of this strategy for increasing overall energy intake have been recorded for numerous other populations as well, including older adults at risk for malnutrition.
From analyzing a broad spectrum of evidence, it appears that the best way to consume more total energy throughout the day is to eat more frequently. While this may benefit a highly active athlete, it’s a recipe for excess adiposity in the average sedentary individual.
Erratic Eating Patterns and Cardiometabolic Risk: Background
The potential negatives of snacking, especially mindless snacking, don’t solely pertain to the ability to drive excess energy consumption and weight gain. These feeding practices can also independently impact your cardiometabolic health.
Before we dive into some direct evidence exploring this hypothesis, it’s important to have a basic grasp of the underlying mechanisms which could be driving these adverse outcomes. To do this, we can look into a domain that combines chronobiology and nutrition. The interplay of these fields of study has been specifically referred to as “chrono-nutrition.”
Most people are generally aware of the concept of circadian rhythms or that our body has its own internal clock and schedule it likes to operate on. This understanding is typically validated by past experiences of jet lag while traveling.
The circadian system orchestrates approximately 24-hour rhythms in metabolism, physiology, and behavior. There is a master clock known as the suprachiasmatic nuclei of the hypothalamus and many secondary clocks located throughout the body such as the brain and peripheral organs (endocrine glands, liver, pancreas, etc.).
It has been proposed that secondary clocks are more flexible and responsive to various cues within our environment. These cues have been specifically termed “zeitgebers” and include things like light, exercise, social interactions, and most notably eating/drinking patterns.
Through the way we eat, we can modify or entrain the internal clock of many peripheral organs which play a crucial role in appetite regulation and the assimilation of nutrients we consume.
With the implementation of a consistent feeding pattern, our circadian clocks will begin to adapt in order to better handle a rush of nutrients. Indeed, several food anticipatory behaviors have been observed in the time leading up to a meal when a fixed meal pattern is adhered to.
For example, if rodents have access to food only during the light phase when they are normally docile, they will adjust to this feeding schedule within a few days and exhibit increased locomotor activity, body temperature, digestive enzyme activity, and gastrointestinal motility a few hours before food becomes available.
Similar findings have been shown in humans during Ramadan. During this period of time (which limits calorie intake to the night), a preprandial rise in plasma levels of cortisol has been documented at dusk before the expected time for eating.
Gut hormones are known to follow a circadian anticipatory pattern to feeding as well. The most notable example of this has been detected in ghrelin, otherwise known as the hunger hormone. Ghrelin has been shown to stimulate gastric acid secretion, gastrointestinal motility, and pancreatic exocrine secretion, all of which increase in anticipation of eating. Numerous studies have documented a rise in ghrelin prior to habitual meal times.
In one such study, participants were divided into a short intermeal interval pattern, with 2.5-3.5 hours between their breakfast and lunch, and a long intermeal interval pattern, with 5.5-6.5 hours between these eating occasions, based on their habitual meal patterns.
During the trial, subjects were provided with breakfast and lunch which matched their typical meal composition and time of consumption. It was found that despite the difference in interval between meals, peak ghrelin concentrations occurred prior to each group’s respective lunch.
In another trial, subjects were placed on a standardized weight maintenance diet for two weeks. Breakfast, lunch, and dinner were consumed at 8 a.m., 12 p.m., and 5:30 p.m, respectively. At the end of the intervention, the participants were brought into the lab for a test-day which consisted of the same dietary protocol. The researchers found that ghrelin rose by an average of 78% before the onset of each meal and fell to trough levels within one hour after the first consumption of food.
More interestingly, this observation that the pattern of ghrelin secretion evolves with an individual’s meal pattern, is reported even under conditions of fasting. Not only will serum concentrations of ghrelin increase at customary mealtimes, but it has also been shown to spontaneously decrease after approximately two hours without the consumption of any food.
Based on these findings, it appears that rather than following a specific rhythm, ghrelin is entrainable; its secretion pattern will ultimately adapt and correspond with a habitual eating schedule. This implies a significant impact of a consistent eating pattern on the ability to control appetite.
With an understanding of how our body has the potential to adapt to an eating schedule, it’s time to look into the direct research on this topic and answer the question – are there different physiological responses to following a consistent meal pattern and an erratic eating pattern?
Erratic Eating Patterns and Cardiometabolic Risk: Evidence
In a randomized cross-over trial in free-living subjects, participants either consumed their usual diet following a regular meal pattern (six meals per day) or an irregular meal pattern. For the irregular meal pattern, the meal frequency averaged out to six meals per day over the course of the intervention but fluctuated day to day in the following order: 7, 4, 9, 3, 5, 8, 6, 5, 9, 8, 3, 4, 7, and 6. Subjects followed each protocol for 14 days and then switched to the other meal pattern.
In the end, it was found that the irregular eating pattern resulted in a lower thermic effect of food, higher plasma total cholesterol, higher plasma LDL concentration, and postprandial insulin insensitivity. In addition, mean energy intake was significantly lower following the regular meal pattern. This suggests that a more regular feeding pattern better controls hunger and this is likely due to the trainability of ghrelin.
This study has since been replicated by another lab. The main difference with this updated trial is its more rigorous methodology. Specifically, all food was provided to the subjects during the intervention period.
The findings from this trial report higher post-meal ratings for hunger and lower postmeal ratings for fullness in the irregular compared with regular intervention period. In addition, a significantly higher postprandial glucose concentration was found in the irregular intervention. The subjects also had a poorer response to an oral glucose tolerance test after the irregular intervention. In combination, these results indicate that following an erratic eating pattern results in a reduction in glucose tolerance, or the ability to clear glucose from the blood, which is associated with an increased risk for type 2 diabetes.
In total, the evidence points towards numerous benefits of following a consistent meal-pattern. Some of these advantages include improved insulin sensitivity and postprandial blood glucose responses, lipid profiles, appetite regulation, and an increased thermic effect of food.
As time has progressed, so has our waistlines. There are a variety of possible explanations for this phenomenon, most of which can be explained by our modern food environment and lifestyle. One specific dietary trend that has climbed in tandem with obesity is snacking.
The data presented displays that humans have forgone a traditional breakfast-lunch-dinner paradigm in exchange for more frequent eating occasions which contribute a smaller amount of energy per feeding. In addition to this finding that humans are eating around the clock, it appears there is a lack of consistency within these incessant caloric events. Together, these behaviors can impose serious consequences on overall health.
Increased feeding frequency, or persistent snacking throughout the day, tends to lead to excess energy consumption and as such, is associated with increased risk of obesity and other comorbidities such as type 2 diabetes. Further, the erratic eating patterns which tend to coincide with snacking have been shown to result in poorer insulin sensitivity, postprandial blood glucose response, lipid profile, and appetite control.
If you are going to snack, do so with purpose. Make it a part of your daily eating regimen rather than something that just happens in response to daily oscillations in food availability. Without keeping a watchful eye over your snacking habits, an erratic eating pattern with a high frequency of feedings is likely to emerge and this is an especially effective recipe for metabolic syndrome.