Dr Martin Juneau, M.D., FRCPCardiologue et Directeur de la prévention, Institut de Cardiologie de Montréal. Professeur titulaire de clinique, Faculté de médecine de l'Université de Montréal. / Cardiologist and Director of Prevention, Montreal Heart Institute. Clinical Professor, Faculty of Medicine, University of Montreal.28 May 2019
Updated May 30, 2019
Our eating habits have changed considerably in recent years. Sometimes for the better, for example by taking advantage of the availability of several foods, ingredients and spices from around the world to diversify our diet and broaden our culinary horizons. But also sometimes for the worse, especially because of a very significant increase in the consumption of ultra-processed industrial foods high in fat, sugar, and salt (see box for the definition of ultra-processed foods). The revolution generated by these “new” foods is particularly remarkable: even though these products did not even exist just a century ago, they currently account for about 50% of all calories consumed by the population.
Unfortunately, most of these ultra-processed products should be considered foods of poor nutritional quality. Not only does their high sugar and fat content give them a very high energy density that promotes the overconsumption of calories, but the use of inexpensive ingredients for their manufacture also ensures that they are deprived of several essential elements found in unprocessed foods (fibres, omega-3s, polyphenols, vitamins, minerals, etc.). For all these reasons, it is recommended that the consumption of these ultra-processed foods be limited as much as possible and that home-cooked meals should be preferred, as proposed in the latest version of Canada’s Food Guide.
The NOVA classification
Instead of the traditional classification of foods according to their content in certain nutrients (proteins, carbohydrates, vitamins), in 2009, Brazilian researchers proposed a new way of categorizing them according to their degree of transformation. This classification, called NOVA, includes four groups:
Group 1: Unprocessed or minimally processed foods
Unprocessed foods can be of plant origin (leaves, shoots, roots, tubers, fruits, nuts, seeds) or animal (meat, eggs, milk). These foods are perishable and must be consumed shortly after their production. These foods are said to be “minimally processed” when they are subjected to certain treatments that increase their shelf life (washing, freezing, pasteurization, etc.) or that modify their taste (yogurt fermentation, coffee roasting), but without altering their nutritional properties.
Examples: fruits and vegetables (fresh, frozen), cereals, mushrooms, meat and fish, seafood, poultry, eggs, pasteurized milk, plain yogurt, coffee, tea, spices, nuts and seeds.
Group 2: Processed culinary ingredients
These products are obtained from group 1 foods through various physical transformations (pressing, grinding, refining). These ingredients are not consumed as is, but rather used in combination with group 1 foods to prepare different dishes.
Examples: vegetable oils, flour, butter, sugar, salt, vinegar.
Group 3: Processed foods
Foods in this group are products made with group 1 foods, to which group 2 substances (salt, oil, sugar, etc.) are added to increase their shelf life, or by using different processes to make them more attractive and palatable. Although these products generally retain the attributes and constituents of the whole foods from which they are derived, their nutritional profile is mostly altered due to the addition of fat, sugar or salt.
Example: canned foods, smoked foods, cured meats, cheeses. It should be noted that alcoholic beverages, which are made by fermentation of foods from the first group, are also part of group 3.
Group 4: Ultra-processed foods
These products are pure industrial creations made from several isolated ingredients. Some of these ingredients are from group 2 (sugar, oil, flour, salt), while others are unknown in nature and manufactured industrially (hydrolyzed proteins, hydrogenated oils, modified starches). Ultra-processed products also contain a wide range of additives to improve their appearance, taste, texture and shelf life (emulsifiers, stabilizers, texturizers, colourants, artificial flavours, sweeteners). In short, ultra-processed products are not foods in the usual sense, but rather a combination of ingredients, designed to give the illusion of a food.
Examples: breakfast cereals, instant soups and noodles, pastries, cakes, breads, various sweet and savoury snacks (cereal bars, cookies, potato chips, crackers, etc.), soft drinks or energy drinks, margarine, candies, “ready-to-eat” food (chicken nuggets or fish, frozen pizza and pasta, etc.).
Ultra-processed foods and weight gain
One of the main arguments against ultra-processed foods is that it has been suspected for several years that their high caloric content could promote the development of obesity. For example, all countries, without exception, that have increased the proportion of ultra-processed industrial foods in their diets must deal with a greater proportion of obese individuals. This is particularly striking in countries in economic transition, where the high availability and low cost of ultra-processed foods mean that the incidence of obesity has skyrocketed, even among the poor.
A remarkable study has just confirmed the close link between ultra-processed food consumption and weight gain. In this randomized clinical trial by Dr. Kevin Hall’s team (National Institute of Health), researchers compared the effects of a diet consisting exclusively of ultra-processed foods to that of a diet based on minimally processed foods. They recruited 20 healthy young people (but who were slightly overweight with an average BMI of 27), and, for a financial compensation of $6,000, the volunteers agreed to be accommodated for 28 consecutive days in the center’s laboratories, with no possibility of going out and with the obligation to eat meals exclusively made from ultra-processed (group 1) or minimally processed (group 2) foods prepared by the research team. In all cases, meals were developed to be equivalent in terms of calories, energy density, fat, sugar and salt, but necessarily differed greatly in the types of sugars and fats present. For example, ultra-processed foods contained significantly more added sugars (54% of total sugars, compared to 1% for unprocessed foods), saturated fats (34% of total fat, compared with 19%), and four times less omega-3s. The subjects were instructed to eat their fill, without worrying about the quantities ingested.
For the first two weeks, each participant ate 3 meals per day from group 1 (ultra-processed foods such as cereals, muffins, white bread or flavoured yogurts for breakfast, deli sandwiches for lunch, and chicken nuggets for dinner) or group 2 (unprocessed foods such as fresh fruits and vegetables, eggs, fish, poultry, whole grains, nuts) (the difference in the types of meals consumed by participants can be viewed here). Snacks were available to volunteers all day long (potato chips, crackers and granola bars for group 1 or nuts, almonds and fruits for group 2). For the next two weeks, the volunteers switched to the other diet, that is, those who ate the ultra-processed foods were now fed the unprocessed foods and vice versa.
The most dramatic result of the study is that the mere fact of being exposed to ultra-processed foods causes a very large increase in the number of calories consumed throughout the duration of the study (Figure 1). Overall, this increase is about 510 kcal per day, the result of an increase in carbohydrate intake (280 kcal/day) and fat intake (230 kcal/day) (but not protein).
Figure 1. Comparison of calorie intake in people on diets of ultra-processed or unprocessed foods. From Hall et al. (2019).
Such a large increase in the calorie intake is obviously not without consequence: the daily weighing of participants shows a rapid increase in body weight which reached 1 kg at the end of the first week of the study (Figure 2). Conversely, people who had eaten the unprocessed diet had lost 1 kg over the course of the study, resulting in a net difference of 2 kg with those fed ultra-processed foods. This is huge, especially considering that these differences can be observed in just two weeks.
Figure 2. Variation in body weight associated with the consumption of ultra-processed or unprocessed foods. From Hall et al. (2019).
Why eat more?
Ultra-processed foods are designed first and foremost to create sensory pleasure (appearance, texture) and satisfy our natural inclination for fat, sugar and salt. It could thus have been expected that the increased intake of these foods by study participants was due to the fact that they preferred to eat these meals rather than those prepared with unprocessed foods. This is not the case, however, as the level of satisfaction of the participants with respect to both food classes was identical, both in terms of appetite and pleasure derived from their consumption. The main difference observed between the two groups is that people ate almost twice as fast when their meals consisted of ultra-processed rather than unprocessed foods (50 kcal/min versus 30 kcal/min). This is probably due to the fact that ultra-processed foods are generally easier to chew and swallow, allowing more food to be ingested in a shorter amount of time and thus excess calories. In this sense, it should be noted that researchers observed that blood levels of peptide YY (a hormone that reduces appetite) were increased in people who ate low-processed foods, while levels of ghrelin (a hormone that stimulates the appetite) were diminished. It is therefore possible that the consumption of ultra-processed food disrupts mechanisms involved in satiety, which promotes overconsumption of food.
These observations strongly suggest that consumption of ultra-processed foods plays a predominant role in the dramatic increase in the incidence of overweight people worldwide. This is truly a major breakthrough that has the potential to revolutionize our understanding of the mechanisms behind this obesity epidemic. For several years, excess weight has always been considered in terms of excessive fat or sugar intake and there are countless “miracle” diets that promise significant weight loss by cutting one or the other. Yet, as we mentioned in another article, there is really no clinically significant difference in the effectiveness of low-fat or low-carb diets in inducing long-term weight loss. Instead of being overly concerned about the amount of fat and/or sugar ingested, Dr. Hall’s study strongly suggests that it is the source of these nutrients that is the most important factor in controlling body weight. To stay slim, the key is to eat unprocessed foods as often as possible and minimize the consumption of ultra-processed industrial foods. Especially since several recent studies have shown that people who regularly consume such foods are at higher risk of cardiovascular disease and premature mortality.
Dr Martin Juneau, M.D., FRCPCardiologue et Directeur de la prévention, Institut de Cardiologie de Montréal. Professeur titulaire de clinique, Faculté de médecine de l'Université de Montréal. / Cardiologist and Director of Prevention, Montreal Heart Institute. Clinical Professor, Faculty of Medicine, University of Montreal.6 May 2019
In Canada, as in most industrialized countries, the proportion of time spent working has decreased considerably since the beginning of the 20th century. At that time, most people worked around 3,000 hours per year (equivalent to 60–70 hours per week), much more than the 1,800 hours worked on average by today’s workers (Figure 1). This reduction in workload was particularly pronounced in Europe, with a 50% drop in hours worked between 1870 and 2000 (and even 60% in some countries such as Germany or Holland). Among the factors responsible for this trend is the importance of the workers’ movements, whose demands made it possible to limit the excesses and abuses that were frequent at the beginning of the Industrial Revolution (10 to 16 hours of work per day, 6 days a week) and to reduce the work week to a maximum of 40 hours.
Figure 1. Decrease in the number of hours worked annually between 1870 and 2000 in Canada (red) and Europe (black). Adapted from Huberman and Minns (2007).
This reduction in workload, however, does not affect all workers: in some countries, there is a significant proportion of people who still work a lot (more than 50 hours per week), a situation that affects more than one in five workers in Turkey, Mexico, Japan and Korea (Figure 2). In Western countries (United Kingdom and the United States) as well as in Australia, long hours at work are also quite frequent (about 15% of workers), while this phenomenon is much less common in Canada as well as in European countries.
Figure 2. Comparison of the proportion of employees who worked more than 50 hours per week in 2016 in different OECD (Organization for Economic Co-operation and Development) countries. From OECD.Stat.
It should also be noted that since the 1990s, deindustrialization and the technological revolution that have affected economically developed countries have fostered the emergence of a new economy, mainly based on services. There are several consequences to this transformation, one of them being that it has become commonplace to work more than 8 hours a day to meet the demands imposed by work. This type of situation is particularly common among high-skilled workers (finance, health, technology, etc.), with more than one in five people routinely working more than 50 hours a week (Figure 3). Lower skilled workers earning lower wages are not spared, however, since many of them have to combine part-time jobs to make ends meet. In other words, even though the majority of people are currently working less than before, there are still two sub-populations of hard workers: highly skilled workers who have to work long hours in exchange for high wages and/or to keep their jobs, and low-skilled, low-wage workers who have to work longer because of their more precarious financial situation.Figure 3. Increase in the proportion of people who work a lot (50 hours a week or more) among highly skilled workers in Western Europe and North America. From Burger (2015).
Effects on cardiovascular health
An immediate consequence of the long hours spent at work is increasing stress levels, a major risk factor for cardiovascular disease. One of the first clues to this comes from the INTERHEART study, where work-related stress was associated with a twice as high risk of coronary heart disease, an increase similar to that observed for well-documented stressors such as divorce or the death of a loved one. This detrimental effect of overwork on health is particularly well documented in Japan. Loyalty, a sense of duty and sacrifice, and respect for the hierarchy occupy a very important place in Japanese culture; as a result, the number of hours spent at work is considered proof of loyalty to the company, and it is therefore very common to work a lot (up to 60 hours or more per week) to please superiors and keep the respect of colleagues. This extreme “dedication” to the company particularly increased in the 1990s because of what has been called the “Lost Decade”, characterized by economic stagnation, lower wages, and greater job insecurity.
During this period, there was a significant increase in mortality caused by overwork, a phenomenon known in Japan as karōshi (karō “overwork” and shi “death”). In most cases, these premature deaths are a consequence of the detrimental influence of long hours worked on the cardiovascular system: for example, an analysis of the causes of death of 203 karōshi victims revealed that 60% had died of a stroke (meningeal or intracerebral haemorrhage and cerebral infarction), 25% had acute heart failure, 13% had a heart attack, and 2% had an aortic rupture. In addition to these sudden cardiac deaths, it should be noted that overwork is also an important cause of suicide (karōjisatsu), which can account for up to 12% of voluntary deaths in Japan. Similar effects of overwork were observed in other Asian countries, including South Korea (gwarosa) and China (guolaosi); in the latter case, it has become common for Chinese companies to introduce what is familiarly known as “996”, that is, a work schedule from 9 a.m. to 9 p.m., 6 days a week.
In Western countries, a meta-analysis of studies of 600,000 workers in Europe, Australia and the United States showed a strong association between long hours worked and the risk of cardiovascular disease. This analysis revealed that people who work a lot (more than 55 hours per week) are about 13% more likely to have a heart attack than those who work 35–40 hours a week, while the risk of stroke was increased by 33%. This increased risk of stroke, already observed among people who work 41–48 hours (10%), increases to 27% among those who work 49–54 hours, and finally reaches 33% among very hard workers (55 hours and more).
Several psychosocial, behavioural and biological factors have been proposed to explain how stress may contribute to the increased risk of cardiovascular events seen in hard workers (Table 1). However, it should be noted that a link between excessive work and these different factors has not been observed in all studies and their exact contribution remains to be clearly established.
Table 1. Major factors that may contribute to the increased risk of cardiovascular disease caused by overwork.
|Risk behaviours (smoking, excess alcohol)||People who work more than 50 hours per week are more likely to smoke (Artazcoz et al. 2009) and drink excessive amounts of alcohol (Virtanen et al. 2015).
|Lack of sleep||Working more than 55 hours per week is associated with an increased risk of not getting enough sleep (twice), having difficulty falling asleep (4 times), and fatigue when waking up (twice). (Virtanen et al. 2009).
|Hypertension||People who work more than 50 hours per week are 30% more likely to have high blood pressure (Yang et al. 2006).
|Sedentary lifestyle||The high number of hours spent at work reduces the time available for other activities, including exercise. Studies show that physical inactivity, combined with sedentary work, increases the risk of cardiovascular disease (Ekelund et al. 2016).
|Fatigue and exhaustion||Young men (<55 years) who had an acute myocardial infarction frequently report episodes of excessive fatigue and exhaustion in the period prior to the coronary heart event (Sihm et al. 1991).
|Job strain||Job strain, a situation where the worker faces high demands but lacks the resources to meet them, is associated with a 23% increase in the risk of coronary heart disease (Kivimäki et al. 2012) and a 30% increase in the risk of stroke (Huang et al. 2015)
|Atrial fibrillation||People who work long hours are at higher risk for episodes of atrial fibrillation, a major risk factor for stroke (Kivimäki et al. (2017).
The increased risk of atrial fibrillation caused by long working hours is particularly interesting because this arrhythmia causes clots in the left atrium, which can reach the brain and obstruct blood flow to the brain, and could contribute to the increased risk of stroke in people who work hard. This increase in the incidence of atrial fibrillation is mainly observed in people who work more than 50 hours a week, and can reach up to 40% of those who work more than 55 hours a week (Figure 4). It should also be noted that overwork has been associated with other coagulation disorders, including deep vein thrombosis (a 68% increase risk), a major cause of pulmonary embolism.
Figure 4. Effect of the number of hours worked on the risk of atrial fibrillation.
From Kivimäki et al. (2017).
Another factor that may contribute to the negative effects of overwork is the so-called job strain, a particular form of stress that has been repeatedly associated with cardiovascular health risk situations. According to the model developed by Robert Karasek (see box), this tension at work is defined as a situation where work and psychological demands are high, combined with a lack of available resources to cope with it and a low decision-making latitude. In other words, a situation where workers are required to be highly productive, but without giving them adequate resources or the necessary flexibility. The risk is further aggravated if the employee has low social support (e.g. from co-workers) and/or if the high productivity requirement is not associated with a valuation of the work done (effort-reward imbalance). It goes without saying that working long hours in such an unfavourable environment can only have a negative impact on both physical and mental health.
A work situation is always the result of a combination of two factors: 1) A “psychological demand”, that is to say, the demands imposed by the job (amount of work to be done, time constraints, interruptions, contradictory demands, etc.); 2) “job decision latitude”, i.e., the ability to make decisions and be creative, for example by having the opportunity to choose how to do one’s job, to participate in decisions, and to use skills. According to Karasek, the combination of psychological demand and decision latitude makes it possible to define 4 types of work situations (see figure below)
The at-risk combination is one in which the psychological demand is high, either because of the amount of work to be done or its difficulty, combined with the depreciation of the workers due to their low participation in the decision-making process.
In conclusion, overwork is associated with a slight but significant increase in the risk of cardiovascular disease, especially stroke. It should be noted, however, that recent studies suggest that the effect of psychological stress on cardiovascular health is more pronounced in people who already have cardiometabolic abnormalities. For example, it has been shown that the association between work strain and risk of premature mortality was higher among those with a history of diabetes, coronary heart disease, or stroke than among those who had not been affected by these conditions. These at-risk individuals generally have several metabolic abnormalities (high blood sugar, inflammation, atherosclerotic plaques) that increase the risk of cardiovascular events following exposure to the effects of work stress (arrhythmia, hypercoagulation, hypertension, etc.). Conversely, people who work hard but who exercise regularly and are in good physical shape do not show any increase in the risk of coronary heart disease. As with the general population, it is therefore important for hard workers to adopt a generally healthy lifestyle (normal weight, plant-rich diet, regular physical activity) to reduce the effects of stress on the risk of cardiovascular events. Working has never killed anyone … who is in good health.