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Want to Lose Weight? Think About When You Eat.

Posted in Science on September 20, 2018

It’s not just the what; it’s also the when. That’s what nutritional scientists are learning as they continue to study the ways in which our diets are complicated by other variables.

One trend that’s emerging, according to a recent write-up in the New York Times, is a body of evidence that connects the outcomes of our diets to our eating schedule and how our eating matches up with our circadian rhythms. Circadian rhythms are the internal clock common to most living things; they’ve been observed in animals, plants, fungi, and bacteria. They take signals from the natural world – the amount of available light, for example – and use that to rough out a daily cycle that regulates biological functions.

One important cue for circadian rhythms, it turns out, is food intake. Glucose levels, enzymes, digestion, internal signals related to hunger and more are tied to the internal cycles of the body. When we eat and when we sleep are both tied up in these signals. Align yourself with these cycles, and you’ll get better results with digestion and sleep. Swim against the stream, sleeping and eating whenever you like, and you may confuse your body – reducing the effectiveness of the sleep that you get, and changing the way that the digestive system processes food.

Circadian rhythm, as the Times article explains, isn’t just a function of a single master clock in the brain. Many of our biological systems have their own timers, working roughly in sync but independently of one another. Insulin, for example, is released more readily during the day, when most people are doing their eating, and slows down after sundown. Other functions related to digestion and eating (including the schedules of the bacteria that live in our guts) are similarly regulated.

If you push back against your natural sleep cycle, your body will likely react in kind. Staying up later than normal several nights in a row confuses your internal mechanisms. Insulin regulation gets sloppier, according to some of the research cited by the Times, and more of the food that you eat will be packed on as fat.

For people whose schedules work against their circadian rhythms, like security guards or gas station clerks assigned to the night shift, these changes can have serious implications. Disruption of insulin sensitivity is a risk factor for metabolic disease and diabetes. Weight gain is a risk factor for diabetes well; it can also lead to obesity and a number of related conditions.

Our bodies are primed for digestion in the morning; that’s when they’re the most sensitive to the appropriate level of insulin to break down glucose in the blood. We’re also primed to release the digestive enzymes that you need to break down food in the morning. The schedule of the body, in fact, dictates that most of our digestive-related resources are on hand for a relatively short window; most of what we need to break down food is available for the eight hours after we wake up.

In light of this, some scientists have recommended that we align our eating and sleeping schedules with our circadian rhythms. Restrict your diet to the eight-hour window of optimal digestion, the thinking goes, and you’ll have a better time of breaking the food down. Less will be converted into fat for the body to store, moving the needle on your bathroom scale to the left; you’ll see a smoother, more coordinated performance when it comes to the delicate interplay between glucose and insulin in the blood.

The link between circadian rhythm and the things that live in our gut has implications for food safety, too. If our body is primed for certain digestive responses at certain times of day, it stands to reason that it might be similarly primed for immune responses – an area that warrants further study. If someone is having trouble breaking down a certain food in their gut and experiences bloating, nausea, or flatulence because of it, it might be because their body wasn’t prepared to break that food down or prepared to do it at that particular time of day.

That’s a medical concern, which makes it a food safety one as well. The same can be said of circadian rhythms and insulin response; although diabetes isn’t what we normally think of when we think of food safety, it’s a medical condition that’s intimately tied up with when and what we eat. The development of diabetes, furthermore, is shaped by what we eat and when. Having diabetes is unsafe; thus, it too is a food safety issue by definition.

Circadian rhythm doesn’t just affect your food, of course: circadian rhythms are intimately tied to our sleep. Eating too late in the day sends mixed messages to the part of the body that determines when we feel tired. This gets back to something that I mentioned earlier: he body doesn’t run on a single clock, but rather has several that each regulate different functions roughly in sync. Generally, the digestive system responds to bright sunlight by priming for some eating. When the sun goes down, the brain releases a hormone called melatonin that primes the body for sleep.

If you’re consistently eating at night, the body is liable to get somewhat confused: the gut will slip out of sync with the brain. The orderly release of melatonin and digestive enzymes both will get somewhat muddled in response.

The details of this phenomenon are still being teased out, but several studies have already been done. Last year, scientists at the University of Texas put mice on carefully controlled feeding schedules to study the relationship between digestion and circadian rhythm. Their findings were written up by the website Science Daily

What they found was remarkable: the time of day that the mice ate was more important to weight loss than the total number of calories ingested. Several groups of the rodents were put on a reduced calorie plan by the scientists. The times at which they were fed, however, were scrambled throughout the day.

Despite their restricted diets, only the mice whose eating times matched natural circadian rhythms lost weight (mice are nocturnal, so their bodies are primed for eating after dark). Feeding the animals reduced-calorie meals during restricted periods left them sleep deprived and wide-awake during the day when they would normally be sleeping.

So: if you’re looking to lose weight, remember to watch the when of your eating alongside the what.

By: Sean McNulty, Contributing Writer (Non-Lawyer)