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Dr Elena Philippou, PhD, RD

26 Nov 2018 - 7 minute read

Chrononutrition: When to eat

Chrononutrition: When to eat

Have you ever thought that when we eat might be as important as what we eat? Read below to find out more!

When, Hippocrates, the ‘father of medicine’ referred to the importance of meal regularity and regularity 400 years BC, no one could have imagined that more than 2,000 years later studies would be published linking meal regularityto metabolic syndrome or that we would be talking about  a term called ‘chrono-nutrition'.

So what is ‘chrononutrition’? Chrononutrition refers to three different aspects of time which are:

1) meal regularity (i.e. the meal is taken at specific times of the day),

2) meal frequency (i.e. the total number of meals and the time between them) and

3) the time (meaning the time the clock shows).

The associationsbetween these aspects of time, diet and health has been studied in animals and humans in order to better understand when we should eat.

Why and how does meal regularity affect health?

Starting with regularity, one might wonder why and in what way meal regularity is related to health. What we know for sure is that the various metabolic processes that take place in our body such as blood glucose regulation, insulin sensitivity, metabolic response after eating, fat metabolism andstorage, detoxificationetc., follow a 24-hour 'circadian rhythm'.

Circadian rhythm

The word ‘circadian' comes from the Latin 'circa' which means 'approximately' and 'diēm' which means 'day'. Circadian rhythm is mainly determined by 2 modes: from the suprachiasmatic nucleus to the hypothalamus which is the central 'clock' that coordinates the peripheral clocks, and the peripheral circadian 'clocks'which are present in almost all organs and cells. Our main clock coordinates the sleep-wake cycle. Peripheral clocks are coordinated by the central clock but are also affected by external factors (called 'zeitgebers') such as light, age and genes.

One of these external factors is food consumption. It is now widely accepted that food consumption and appetite, digestion and metabolism of food, follow a circadian rhythm.

On the other hand, food consumption affects the peripheral clock with effects on the liver and intestines, while the central clock affects the absorption of food.

So if we eat at regular times which don’t change from one day to the next, the messages on our biological clock will also be received at regular times. In the opposite case, where meals are taken at irregular times, or there is a irregularity in meal intake, our biological clock is disturbed and this increases the chance of metabolic syndrome.

Metabolic syndrome is a combination of many risk factors for cardiovascular problems and diabetes such as increased fat around the waist (visceral fat), high blood pressure, low 'good' (HDL) cholesterol and high triglyceride concentration.

An example of ‘disturbed’ circadian rhythm

An extreme example of circadian rhythm disturbance is shift work, especially for people who work at night. Numerous studies have shown that these individuals have an increased chance of developing cancer, cardiovascular problems and metabolic syndrome, while in 2007, the World Health Organization and the International Agency for Research on Cancer concluded that shift work is likely to disrupt the circadian rhythm. Working in shifts for at least 20-30 years was also associated with a 40-50% increase in the risk of breast cancer (for other cancers the relationship is not so clear) while these individuals have an increased risk of myocardial infarction (23%), coronary heart disease. disease (24%) and stroke (5%) in relation to people who do not work shifts, even when other factors are taken into account. The above effects are believed to be related to the internal desynchronization resulting from the changes in the sleep-wake cycle. Of course, lack of sleep is considered an important factor, but some of the above effects are thought to be related to irregular meals.

Irregular meals and metabolic syndrome

How much do irregular meals affect the likelihood of metabolic syndrome? To investigate this scientificquestione in greater depth, Dr Gerda Pot studied the meals of the population of the 1946 birth cohort by the University of London and the UK Medical Research Council. This study involved people born in the same week in 1946 and their meal intake at age 53. Irregular meals were determined by the difference in energy intake per meal compared to the 5-day average energy intake at the same meal. Scores were calculated for each meal and snack and the total of the day. It appeared that people who had more irregular energy intake in the morning were more likely to have metabolic syndrome than those who had a more stable intake. That is, if one consumes. 700 calories for breakfast one day, the next day 200 kcals at that meal and the third daydoes not eat breakfast, then they are more likely to have metabolic syndrome than another person who consumes a breakfast containing a similar amount of energy each day.

There have also been other studies examining the effect of irregular meal frequency on lipids, glucose, insulin and uric acid in 10 thin and 10 obese (healthy) women. An intervention study was conducted in 2 phases of 14 days where women either consumed their usual diet in 6 regular meals or in meals that differed in frequency (3-9 meals per day). In thin women, it appeared that the maximum concentration and insulin curve in a control meal consumed after the intervention period were higher after the period of irregular meals. Obese women had a reduced insulin concentration at a control meal consumed after the period of regular meal consumption.  The regular meal consumption period was also characterized by lower energy intake, increased postprandial thermogenesis and lower total and LDL cholesterol. What all this means is that meal regularity improves metabolism and helps reduce the health problems associated with diabetes and cardiovascular disease.

Does when we eat matter?

One might also ask, 'Does when we eat matter?' And the answer comes through an oldsaying: ‘Eat breakfast like a king, lunch like a prince and dinner like a beggar’. Many studies have shown that eating breakfast helps reduce total calorie intake during the day, lowers total and 'bad' cholesterol, but also helps maintain body weight. It is good to know that every time we eat our metabolism  increases by about 10% of what we consume by the production of heat, something called ‘post-meal thermogenesis’. If our meal contained 400 calories, about 40 calories would be used to metabolize the meal. So it has been shown that we have a greater increase in postprandial metabolism after eating the same meal in the morning compared to the evening, while at night digestion and gastric emptying are less effective. We all know that heavy meals at night affect the quality and duration of sleep, and when we don’t sleep enough our energy intake and likelihood of obesity increase. And while we used to say that only the total number of calories consumed in a day mattered, there is now research showing that eating a low-calorie diet leads to a greater weight loss in people who consume the most calories at  breakfast and lunch and the least at dinner compared to the opposite.

Frequency of meals and effects on metabolism

At lastly, what is the role of meal frequency in health? Research results are not so clear on this issue. What we know empirically however, is that the long intervals between meals usually increase the energy intake at the next meal and cause a feeling of loss of control over the amount and / or quality of the food taken at that meal resulting in long-term weight gain. At the same time, if we have big gaps between meals our metabolic rate falls inan effort to protect us from the supposed ‘starvation’ that it thinks we are going through. After all, our ancestors who gave us their genes were the people who managed to survive under adverse starvation conditions.

Chrononutrition rules:

In conclusion, chrononutrition means that we should not only think about what we eat but also whenwe eat it, how often we eat and keep a steady schedule from one day to the next. This is not always possible due to the ‘social jetlag’ that creates a mismatch between our biological clock and social circumstances e.g. if we are invited to dinner late at night. However, we can try to follow some chrononutrition rules most of the time as they will contribute to our health and quality of life such as:

1) always eat breakfast

2) eat something (a meal or snack) every 3-4 hours

3) eat the biggest meal of the day at noon and not at night

4) eat most of our most calories before dinner,and

5) eat a small dinner (the smallest meal of the day)

So try to follow these chrononutrition rules or make even a small change in your schedule and you will feel the benefits very soon.



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Elena Philippou Diet and Nutrition

Chrononutrition: When to eat

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