Eating by your biological clock

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It's common for people to ply health and nutrition experts for insider tips, secrets or tricks for weight loss. Our common response to these entreaties is very unsatisfying to most: There's no magic formula. Just eat less overall, and less junk in particular.

This tried and true conventional wisdom still holds true for sure, and there's no getting around it. But what if you are already eating a reduced calorie diet – one that by all calculations should be promoting weight loss – but the scale simply isn't budging?

This is a situation I often encounter with my patients, and the trick to breaking through the plateau often lies with changing when they're eating which calories during the day. Specifically, in the context of an appropriately lower calorie diet, you may be able to accelerate weight loss and significantly improve other markers of metabolic health by following three simple rules:

  1. Never skip breakfast, and always make sure it includes a healthy carbohydrate.
  2. Be sure to front-load the majority of your calories and carbs to the first half of the day so you've consumed the majority of your day's food by mid afternoon.
  3. Make dinner a small, low-calorie, low-carb meal – eating lean protein and non-starchy vegetables.

This advice flies in the face of a commonly held dogma that a calorie is a calorie, no matter what time of day you consume it, and that weight loss boils down to a simple math equation of consuming fewer calories than you expend.

In fact, there is now emerging evidence that people who consume the exact same diets in terms of calories and macronutrients – carbs, protein and fat – may see very different results on the scale and in terms of blood sugar control, triglycerides and even cholesterol levels, depending on how they distribute their food intake throughout the day. It seems to be metabolically favorable to consume most of our calories and carbs in the early part of the day, compared to consuming the majority of them in the evening. But why?

The answer lies in a part of our brain called the hypothalamus, which houses a cluster of nerves that govern a "master biological clock," also known as circadian rhythms. In response to different cues, most notably light and dark, the master clock up-regulates or down-regulates genes that produce the hormones, enzymes and cell receptors responsible for metabolizing and storing carbohydrates and fat.

In the morning, people seem most sensitive to the effects of insulin, requiring less of this hormone in order to clear our blood of the sugar produced from a higher carb meal. At night, we are less sensitive to insulin, resulting in higher blood sugar levels, higher levels of insulin secreted and increased amounts of fat storage in response to higher carbohydrate meals.

This effect has been demonstrated in both animals and humans; in both lean and obese people; and in healthy people as well as those with Type 2 diabetes. Because insulin is an "anabolic" hormone, it promotes storage and retention. This makes it difficult for us to burn stored carbohydrates and fat for energy. Having chronically high levels of insulin circulating, therefore, can have an effect on our weight in the longer term. Clearly, this does not bode well for those of us used to large pasta and rice-based dinners and grazing well into the evening!

A related phenomenon that has recently been demonstrated in both healthy, lean people and overweight people with Type 2 diabetes is called "the second meal effect." The second meal effect refers to differences in the body's metabolic response to your lunch, the second meal, based on whether you ate breakfast – and possibly also what you ate for breakfast.

Specifically, when people eat a substantial breakfast – particularly one containing at least 50 percent carbohydrates – it seems to result in significantly lower post-lunch hyperglycemia and insulin levels compared to when the same people eat the same exact lunch after having skipped breakfast. This effect also has been demonstrated to last beyond lunch, exerting an effect on post-dinner blood sugar levels as well. The second meal phenomenon may explain why a substantial body of observational research has found a correlation between skipping breakfast and both obesity and Type 2 diabetes.

Because the science is still so hot-off-the-press when it comes to the apparent benefits of eating in sync with the circadian clock, researchers haven't yet nailed down a formula for how we should organize our meals for optimal metabolic health. We don't yet know, for example, what specific percentage of our calories we should consume before dinner. Is it 60 percent? Seventy-five percent? Eighty-five percent?

We also don't know whether there's a specific time of day after which we should ideally not eat at all. And if there is, does that time of day vary based on daylight savings or latitude? Is there an optimal percentage of our calories we should get from carbohydrates at breakfast or lunch? And stepping back, would a circadian-synced eating pattern be equally beneficial for all types of people – such as, say, vegans and vegetarians whose plant-based diets may be far less energy dense overall despite being relatively high in carbohydrates? What about for people of varying ethnic backgrounds?

Interventional research on how circadian-synced eating patterns affect weight and health outcomes in people is still in its infancy, and to date the longest-term intervention study on these eating patterns in people has only been about three months. I've had patients in my clinical practice following this dietary pattern who have achieved terrific results in periods of time ranging from six months to a year and maintained their losses well past a year – and counting. But until we have some longer term and varied studies to consult, clear answers to many of these questions remain elusive. Still, while we wait for more evidence-based guidance, shifting your current meal patterns to align with the old adage, "breakfast like a king, lunch like a prince, dinner like a pauper," may be sufficient to help you gain some momentum on your weight-loss journey if you find yourself stuck in a rut.

Copyright 2015 U.S. News & World Report

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