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更新时间:2019/3/10 10:42:18 来源:纽约时报中文网 作者:佚名

Is breakfast really the most important meal of the day?

Along with old classics like ‘carrots give you night vision’ and ‘Santa doesn’t bring toys to misbehaving children’, one of the most well-worn phrases in the arsenal of tired parents everywhere is that breakfast is the most important meal of the day. Many of us grow up believing that skipping breakfast is a dietary travesty – even if only two thirds of adults in the UK eat breakfast regularly, according to the Association of UK Dieticians (BDA), and around three-quarters of Americans.


The clue for why breakfast is supposed to be important is in its name: we’re advised to eat it to break our overnight fast.


“The body uses a lot of energy stores for growth and repair through the night,” explains dietician Sarah Elder. “Eating a balanced breakfast helps to up our energy, as well as protein and calcium used throughout the night.”

营养学家埃尔德(Sarah Elder)解释说,“在夜间,身体动用了大量的能量储备进行生长和修复,吃上一顿营养均衡的早餐,有助于补上我们夜间所消耗的能量,以及蛋白质和钙。”

But there’s widespread disagreement over whether breakfast should keep its top spot in the hierarchy of meals. As well as the rising popularity of fasting diets, there have been concerns around the sugar content of cereal and the food industry’s involvement in pro-breakfast research – and even one claim from an academic that breakfast is “dangerous”.


So what’s the reality? Is breakfast a necessary start to the day… or a marketing ploy by cereal companies?


Weighty decision


The most researched aspect of breakfast (and breakfast-skipping) has been its links to obesity. Scientists have different theories as to why there’s a relationship between the two.


In one US study that analysed the health data of 50,000 people over seven years, researchers found that those who made breakfast the largest meal of the day were more likely to have a lower body mass index (BMI) than those who ate a large lunch or dinner. The researchers argued that breakfast helps increase satiety, reduce daily calorie intake, improve the quality of our diet – since breakfast foods are often higher in fibre and nutrients – and improve insulin sensitivity at subsequent meals, which can be a risk for diabetes.


But as with any study of this kind, it was unclear if that was the cause – or if breakfast-skippers were just more likely to be overweight to begin with.


To find out, researchers designed a study in which 52 obese women took part in a 12-week weight loss programme. All had the same number of calories over the day, but half had breakfast, while the other half did not.


What they found was that it wasn’t breakfast itself that caused the participants to lose weight: it was changing their normal routine. The women who said before the study that they usually ate breakfast lost 8.9kg when they stopped having breakfast, compared to 6.2kg in the breakfast group. Meanwhile, those who usually skipped breakfast lost 7.7kg when they started eating it – and 6kg when they continued to skip it.


If breakfast alone isn’t a guarantee of weight loss, why is there a link between obesity and skipping breakfast?


Alexandra Johnstone, professor of appetite research at the University of Aberdeen, argues that it may simply be because breakfast-skippers have been found to be less knowledgeable about nutrition and health.

阿伯丁大学(University of Aberdeen)研究食欲的教授约翰斯通(Alexandra Johnstone)认为,这可能只是因为不吃早餐的人,对营养和健康的知识了解比较少。

“There are a lot of studies on the relationship between breakfast eating and possible health outcomes, but this may be because those who eat breakfast choose to habitually have health-enhancing behaviours such as not smoking and regular exercise,” she says.


A 2016 review of 10 studies looking into the relationship between breakfast and weight management concluded there is “limited evidence” supporting or refuting the argument that breakfast influences weight or food intake, and more evidence is required before breakfast recommendations can be used to help prevent obesity.


Feast or fast?


Intermittent fasting, which involves fasting overnight and into the next day, is gaining ground among those looking to lose or maintain their weight or improve their health.


One pilot study published in 2018, for example, found that intermittent fasting improves blood sugar control and insulin sensitivity and lowers blood pressure. Eight men with pre-diabetes were assigned one of two eating schedules: either eating all their calories between 9:00 and 15:00, or eating the same number of calories over 12 hours. The results for the 9:00-15:00 group were found to be on par with medicine that lowers blood pressure, according to Courtney Peterson, the study’s author and assistant professor of nutrition sciences at the University of Alabama at Birmingham.

例如,2018年发表的一份试点研究发现,间歇性禁食可以改善血糖控制和胰岛素敏感性,并降低血压。8名前期糖尿病患者被安排了两种饮食计划:一种在9点到15点之间摄入全部卡路里,另一种在12个小时内摄入相同数量的卡路里。该研究的作者、亚拉巴马大学伯明翰分校(University of Alabama at Birmingham)营养科学助理教授彼得森(Courtney Peterson)说,研究结果发现,9点到15点那一组的结果与降压药不相上下。

Still, the study’s small size means more research is needed on its possible long-term benefits.


If skipping breakfast (and other food outside of a restricted time slot) could potentially be good for you, does that mean breakfast could be bad for you? One academic has said so, arguing that breakfast is ‘dangerous’: eating early in the day causes our cortisol to peak more than it does later on. This causes the body to become resistant to insulin over time and can lead to type 2 diabetes.


But Fredrik Karpe, professor of metabolic medicine at Oxford Centre for Diabetes, Endocrinology and Metabolism, argues this isn’t the case. Instead, higher levels of cortisol in the morning are just part of our body’s natural rhythm.

但牛津大学糖尿病、内分泌及代谢病中心(Oxford Centre for Diabetes, Endocrinology and Metabolism)的代谢医学教授卡普(Fredrik Karpe)就认为,情况并非如此。相反,皮质醇水平在早上升高只是我们身体自然节奏的一部分。

Not only that, but breakfast is key to jumpstarting our metabolism, he says. “In order for other tissues to respond well to food intake, you need an initial trigger involving carbs responding to insulin. Breakfast is critical for this to happen,” Karpe says.


A randomised control trial published last year involving 18 people with, and 18 people without, diabetes found that skipping breakfast disrupted the circadian rhythms of both groups and led to larger spikes in blood glucose levels after eating. Eating breakfast, the researchers conclude, is essential for keeping our body clock running on time.


Peterson says those who skip breakfast can be divided into those who either skip breakfast and eat dinner at a normal time – getting the benefits of intermittent fasting, if not breakfast – or those who skip breakfast and eat dinner late.


“For those who eat dinner later, their risk of obesity, diabetes and cardiovascular disease goes through the roof. While it seems breakfast is the most important meal of the day, it might actually be dinner,” she says.


“Our blood sugar control is best early in the day. When we eat dinner late, that’s when we’re most vulnerable because our blood sugar is worst. There’s more research to do, but I’m confident you shouldn’t skip breakfast and have dinner late.”


She says we should think of our circadian rhythm as an orchestra.


“There are two parts of our circadian clock. There’s the master clock in the brain, which we should think of as analogous to a conductor of an orchestra, and the other half is in every organ, which has a separate clock,” she says.


And that ‘orchestra’ is set by two outside factors: bright light exposure and our eating schedule.


“If you’re eating when you’re not getting bright light exposure, the clocks that control metabolism are in different time zones, creating conflicting signals as to whether to rev up or down.”


It’s like two halves of an orchestra playing different songs, Peterson explains, and this is why eating late impairs blood sugar and blood pressure levels.


Researchers from the University of Surrey and University of Aberdeen are halfway through research looking into the mechanisms behind how the time we eat influences body weight. Early findings suggest that a bigger breakfast is beneficial to weight control.

来自英国萨里大学(University of Surrey)和阿伯丁大学的研究人员正在研究进食时间如何影响体重的原理。早期的研究表明,丰盛的早餐有助于控制体重。

Health food


Breakfast has been found to affect more than just weight. Skipping breakfast has been associated with a 27% increased risk of heart disease, a 21% higher risk of type 2 diabetes in men, and a 20% higher risk of type 2 diabetes in women.


One reason may be breakfast’s nutritional value – partly because cereal is fortified with vitamins. In one study on the breakfast habits of 1,600 young people in the UK, researchers found that the fibre and micronutrient intake, including of folate, vitamin C iron and calcium, was better in those who had breakfast regularly. There have been similar findings in Australia, Brazil, Canada and the US.


Breakfast is also associated with improved brain function, including concentration and language. A review of 54 studies found that eating breakfast can improve memory, though the effects on other brain functions were inconclusive. However, one of the review’s researchers, Mary Beth Spitznagel, says there is “reasonable” evidence breakfast does improve concentration – there just needs to be more research.

早餐还能改进大脑功能,包括提高注意力和语言能力。一篇对54项研究的文献综合分析发现,吃早餐可以改善记忆,但对大脑其他功能的影响尚无定论。然而,该论文的作者之一施皮茨纳格尔(Mary Beth Spitznagel)表示,有“合理的”证据表明,早餐的确可以提高注意力,只是还需要更多的研究。

“Looking at studies that tested concentration, the number of studies showing a benefit was exactly the same as the number that found no benefit,” she says.


“And no studies found that eating breakfast was bad for concentration.”


What’s most important, some argue, is what we eat for breakfast.


High-protein breakfasts have been found particularly effective in reducing food cravings and consumption later in the day, according to research by the Australian Commonwealth Scientific and Industrial Research Organisation.

澳大利亚的联邦科学与工业研究组织(Commonwealth Scientific and Industrial Research Organisation)的研究发现,蛋白质含量丰富的早餐,对于降低当天随后时间的食欲及减少食物摄取量,特别有效。

While cereal remains a firm favourite among breakfast consumers in the UK and US, a recent Which? investigation into the sugar content of ‘adult’ breakfast cereals found that some cereals contain more than three quarters of the recommended daily amount of free sugars in each portion, and sugar was the second or third highest ingredient in seven out of 10 flaked cereals.


But some research suggests if we’re going to eat sugary foods, it’s best to do it early. One study found that changing levels of the appetite hormone leptin in the body throughout the day coincide with having our lowest threshold for sweet food in a morning, while scientists from Tel Aviv University have found that hunger is best regulated in the morning. They recruited 200 obese adults to take part in a 16-week-long diet, where half added dessert to their breakfast, and half didn’t. Those who added dessert lost an average of 40lbs (18kg) more – however, the study was unable to show the long-term effects.

但一些研究表明,如果我们要吃甜食,最好早点吃。一项研究发现,人体内的食欲荷尔蒙瘦素的水平在一天当中是处在不断变化中的,早间摄入甜食的门槛最低。特拉维夫大学(Tel Aviv University)的科学家发现,饥饿感在早上控制得最好。他们招募了200名肥胖的成年人参加了为期16周的节食,一半人的早餐中加了甜点,另一半则没有。那些加入了甜点的,平均减掉了40磅(18公斤),不过,这项研究无法证实其长期效果。

A review of 54 studies found that there is no consensus yet on what type of breakfast is healthier, and conclude that the type of breakfast doesn’t matter as much as simply eating something.


Final take


While there’s no conclusive evidence on exactly what we should be eating and when, the consensus is that we should listen to our own bodies and eat when we’re hungry.


“Breakfast is most important for people who are hungry when they wake up,” Johnstone says.


For instance, research shows that those with pre-diabetes and diabetes may find they have better concentration after a lower-GI breakfast such as porridge, which is broken down more slowly and causes a more gradual rise in blood sugar levels.


Every body starts the day differently – and those individual differences, particularly in glucose function, need to be researched more closely, Spitznagel says.


In the end, the key may be to be mindful of not over-emphasising any single meal, but rather looking at how we eat all day long.


“A balanced breakfast is really helpful, but getting regular meals throughout the day is more important to leave blood sugar stable through day, that helps control weight and hunger levels,” says Elder.


“Breakfast isn’t the only meal we should be getting right.”