Nutritional challenges and health implications of takeaway and fast food

Abstract

Introduction

Lifestyle changes that have taken place in many countries worldwide over the last few decades have been shown to impact food consumption patterns. ^1,–4 One of the most prominent trends is the increasing frequency with which meals are consumed outside of the home environment. ^4,–6 In addition, even meals consumed at home are often purchased from catering outlets that offer takeaway or home delivery service. ⁵ , ⁷ The traditional family dinner is increasingly being replaced by eating “on the run” at various locations throughout the day. ¹ As a result, less time is spent on food preparation, with an average woman and man in the United States spending 47 min and 19 min per day, respectively, carrying out food preparation and cleaning up. Moreover, among the 13,200 US citizens in one study, 59% of men and 32% of women did not spend any time on daily food preparation. ⁸

Food eaten outside of the home is becoming an important and regular component of the Western diet. ^9,10 A number of studies have shown increased frequency of takeaway and fast food consumption worldwide, especially in Europe, the United States, and Australia. ^9,–15 A governmental report in the United Kingdom indicated about 22% of residents were found to purchase foods from takeaway outlets at least once a week and 58% a few times a month. ¹¹ A similar frequency of consumption of takeaway or fast food has also been observed in other countries, with approximately 28% of Australians ¹² consuming takeaway meals at least twice a week and 37% of US residents ¹³ eating fast food at least once over two nonconsecutive days. Fast food is particularly popular among adolescents, with a report from 2001 indicating that 75% of US teenagers between the ages of 11 and 18 years eat at fast-food outlets at least once a week ¹⁴ and a 2010 report indicating that 70% of Brazilian students (9–18 years old) consume fast food four times or more per week. ¹⁵ Moreover, Guthrie et al. ¹⁰ reported that consumption of fast food among children has increased from 2% of total energy in the 1970s to 10% of energy in the 1990s. ¹⁰ That observed trend is continuing among children and adolescent populations, with data from the 2003–2006 National Health and Nutrition Examination Surveys showing a further increase to 13% of total daily energy intake. ¹⁶

It is well known that food plays an important role in the development and prevention of many diseases. ¹⁷ There is also no doubt that observed changes in dietary patterns affect the quality of the diet as well as public health. Consumption of takeaway and fast food has been shown to have adverse health effects, and while the majority of studies on this subject have focused on the relationship between fast food consumption and weight gain, ^18,–20 more frequent consumption of meals prepared outside of the home has also been observed to correspond with increased risk of insulin resistance, type 2 diabetes, elevated total cholesterol, and low-density lipoprotein cholesterol (LDL-C) levels as well as decreased high-density lipoprotein cholesterol (HDL-C) concentrations. ¹⁸ , ^21,22 Takeaway or fast food consumers are characterized by higher intakes of energy, fat, saturated fatty acids (SFAs), trans fatty acids (TFAs), added sugar and sodium, and lower intakes of fiber, macronutrients, and vitamins in comparison to those who do not eat food prepared outside the home. ¹³ , ¹⁹ , ^23,24 Additionally, takeaway and fast-food consumption has been linked to poor dietary patterns including higher intakes of carbonated soft drinks and sweets and lower consumption of fruits, vegetables, whole grains, and dairy products. ^12,13 , ¹⁹ , ²⁴

This review focuses on the energy and fat content in takeaway and fast foods and their health implications. However, it should be pointed out that other components of takeaway and fast foods, such as salt and sugar, also have important effects on health.

Methods

Literature searches were performed using the following electronic databases: Medline, ScienceDirect, and Web of Science. The following key words were used: fast food, takeaway food, nutrient content, lifestyle, health, obesity, cardiovascular disease, blood lipids, fat, saturated fatty acids, trans fatty acids, energy density, food consumption patterns, diet quality. In addition, the reference list of each original and review article identified was searched for additional references. Searches were restricted to manuscripts in the English-language literature and included all available data until March 2011. Articles were limited to human participants only.

Energy and Energy Density

Humans possess a weak initial ability to recognize the energy density of consumed food and to appropriately regulate the bulk of food eaten to maintain energy balance; thus, people generally tend to consume a similar amount of food every day regardless of variations in energy density. ^25,–27 This tendency to consume a constant amount of food was confirmed by Seagle et al., ²⁸ who analyzed the 4-day food records of normal-weight adults. Daily variations in the weight of consumed food were significantly smaller than variations in the intake of either energy or fat. ²⁸ Similarly, a retrospective investigation of three community studies from the United Kingdom (the Cambridge Family Food Survey, n  = 195); the MRC National Survey of Health and Development [NSHD], n  = 343; and the Leeds Nutritional Survey, n  = 2,086) showed that the weight of food consumed remained relatively constant over a 7-day period. ²⁹ However, when food with a low energy density is eaten, a greater amount of food needs to be consumed for a given level of energy intake in comparison to food with a high energy density. Therefore, increasing the energy density of the diet may result in a passive increase in energy intake, because people are generally habituated to eat a relatively constant weight of food.

Bell et al. ²⁶ conducted a study of normal-weight women ( n  = 18) who consumed all of their meals in the laboratory over three 2-day periods. During lunch, dinner, and an evening snack, participants consumed ad libitum main entrees, which were similar in macronutrient composition but varying in energy density (low, medium, or high). The women consumed similar amounts of food independent of the energy density of the meal served. Thus, energy intake was about 25% lower with meals of low energy density in comparison with those of high energy density. Results showed no differences across conditions in hunger or fullness before meals, after meals, or over each 2-day period. ²⁶ These findings were confirmed by several other studies that tested the effect of variations in the fat content of the diet while maintaining a constant energy density. ^30,31 Stubbs et al., ³⁰ in a 14-day intervention study, reported that men who were offered a diet varying in fat content (20, 40, and 60% of total energy) but with a constant energy density, ate a constant weight of food; therefore, they had similar energy intakes despite different proportions of fat content in the diet. Similarly, in a randomized crossover study performed over an 11-day period, Saltzman et al. ³¹ found that seven pairs of male twins who consumed, ad libitum , a low- or a high-fat diet matched for energy density (20% or 40% of total energy) had similar daily energy intakes (10.3 and 10.7 MJ/d, respectively) regardless of the condition of the diet. These findings support the hypothesis that the energy density of consumed food is a crucial determinant of energy intake. Therefore, the weight or volume of food consumed, and, thus, the energy density, may increase or decrease energy intake independent of the macronutrient content of the diet.

Relationship between Takeaway and Fast Foods and Obesity

The relationship between fast or takeaway food consumption and increased body mass index (BMI) and obesity has been reported in many epidemiological studies. ^18,–20 , ³² Among a Spanish population ( n  = 3,054), Schröder et al. ³³ found that consumption of fast food more frequently than once a week increased the risk of being obese by 129%. These results are consistent with the findings of Kjøllesdal et al., ³⁴ who reported from a group of working Oslo citizens ( n  = 8,943) that the likelihood of being obese increased significantly with frequent eating in staff canteens, after demographic and socioeconomic variables were taken into account. Similar trends have also been observed in developing countries; Rouhani et al. ³⁵ found that high intakes of fast foods were significantly associated with increased incidences of overweight and obesity among Isfahani (Iranian) girls aged 11–13 years.

Furthermore, consumption of fast foods two times or more per week has been independently associated with a 31% higher prevalence of moderate abdominal obesity in men and a 25% higher prevalence in women. ¹⁹ According to a theoretical model, an energy increase of 17 kcal/day for men and 19 kcal/day for women would lead to a weight increase of 1 kg per year independent of baseline body weight. ³⁶ On average, regular consumption of fast-food meals was related to increases in energy intake of 56 kcal/day ³⁷ and 187 kcal/day ¹⁹ among adults and children, respectively. Thus, a higher frequency of fast-food consumption was associated with a weight gain of 0.72 kg over 3 years, ³⁷ and of 4.5 kg over a 15-year period, ¹⁸ above the average weight gain. Moreover, women who reported eating takeaway food once a week were 15% less likely to be weight maintainers than those who rarely (once a month or less) or never ate takeaway food. ³⁸

Energy Content and Intake of Takeaway and Fast Foods

It has been shown that a typical meal purchased from fast-food restaurants tends to be energy dense and contains approximately 236 kcal/100 g, which is twice the recommended energy density of a healthy diet. ³⁹ Considering the large portion sizes of meals eaten out of the home, one meal can provide approximately 1,400 kcal. ⁴⁰ Bauer et al. ⁴¹ found that despite the increasing attention to the role of fast food in the American diet, including legislation and public health campaigns addressing the healthfulness of fast food, the median energy content across all menu items remained relatively stable over a 14-year study period (1997–2010).

Mancino et al. ⁴² based on the dietary recall data collected over2 nonconsecutive days from the 2003–2004 National Health and Nutrition Examination Survey (NHANES) and the 1994–1996 Continuing Survey of Food Intakes by Individuals, and with the use of a first-difference estimator, found that each meal eaten away from home added, on average, 130 kcal to total daily energy intake, with lunch and dinner having the greatest effect on total daily energy. French et al., ¹⁴ in a study conducted among 11–18-year-old American teenagers ( n  = 4,746), reported that energy intake was 40% higher among male and 37% higher among female adolescents who reported eating fast food three times or more during the studied week in comparison with those who had not eaten fast foods. Additionally, a dose-response pattern was observed with energy intake directly increasing with increased frequency of fast food consumption. ¹⁴ Similarly, a follow-up study including African American women aged 30–69 years ( n  = 44,072) indicated that, compared to women who have never eaten Chinese food, pizzas, fried fish, fried chicken, or burgers, women who reported eating such foods at least once a week had significantly higher daily energy intakes. ²¹ Furthermore, a study by Bowman and Vinyard ¹⁹ that included 9,872 adults aged 20 years and older showed a positive relationship between the energy density of the diet and fast food consumption. Their evaluation of the quality of the diet of American adults showed increased dietary energy density among men and women who reported eating fast food (95 and 102 kcal/100 g, respectively) compared to those who did not (89 and 98 kcal/100 g among men and women, respectively). ¹⁹

Total Fat and Saturated Fatty Acids

The high levels of fat intake commonly associated with takeaway or fast food consumption may be a factor leading to obesity development that is independent of total energy intake. Findings of a study carried out by Alfieri et al. ⁴³ among 150 adults in the United Kingdom found a strong positive correlation between BMI and total fat consumption but no association with energy intake. These results were in line with findings of a cross-sectional study of 15,266 men (55–79 years) performed by Satia-Abouta et al., ⁴⁴ which showed that fat intake has a higher adipogenic effect than total energy intake. In a multivariate linear regression model after adjustment for demographic and health-related characteristics, BMI increased by 0.14 and 0.53 kg/m ² for every 500 kcal of total energy intake and 500 kcal energy derived from fat, respectively. Additionally, only energy provided from fat, but not energy from other macronutrients (carbohydrate and protein), increased linearly with increasing BMI. In contrast, Larson et al. ⁴⁵ suggested that dietary fat plays a very minor role in increasing adiposity, and explained only 2% of variation in body fat after controlling for other obesity risk factors.

There are several possible explanations for why dietary fat intake may be associated with body weight gain. A number of studies have shown that fat exerts a less satiating effect than either carbohydrate or protein. Cotton et al. ⁴⁶ found that a carbohydrate-supplemented breakfast (173.4 g of carbohydrate, 11.2 g of fat, 12.7 g of protein, and 803 kcal of total energy) suppressed intake of food with the next meal, in contrast to the breakfast supplemented by fat (77.8 g of carbohydrate, 50.9 g of fat, 12.7 g of protein, and 803 kcal total energy), which produced no detectable effect on appetite expression. Furthermore, fat is utilized with very high energy efficiency; thus, the diet-induced thermogenesis following fat consumption is much lower than after protein or carbohydrate intakes. Also, a high-fat meal does not enhance lipid oxidation, and may, therefore, promote dietary fat accumulation in adipose tissue. In a study by Bennett et al., ⁴⁷ the addition of 50 g of fat to a standard breakfast (55% energy from carbohydrate, 30% from fat, and 15% from protein) did not increase fat oxidation or energy expenditure either during the immediate 6 h postprandial period or over the following 18 h. Similarly, Horton et al. ⁴⁸ found that in a group of 16 men who were offered 14 days of isoenergetic overfeeding (50% above energy recruitment) of fat and carbohydrate, overfeeding with fat did not produce an increase in fat oxidation and total energy expenditure, and led to storage of 90–95% of excess energy. In contrast, carbohydrate overfeeding was associated with increased carbohydrate oxidation and total energy expenditure and resulted in 75–85% of excess energy being stored. ⁴⁸ Furthermore, Raben et al. ⁴⁹ in a study of 19 healthy participants who were provided with meals similar in energy density but rich in protein, fat, carbohydrate, or alcohol observed that postprandial lipid oxidation was suppressed after protein-, carbohydrate-, and alcohol-rich meals and was almost unchanged after the fat-rich meal. Griffiths et al. ⁵⁰ reported that lipid oxidation was higher after a high-fat meal (80 g of carbohydrate, 80 g of fat, and 18 g of protein) than after a low-fat meal (80 g of carbohydrate, 0.8 g of fat, and 18 g of protein), but the difference in oxidation level reached 10 g only (20.7 vs. 10.6 g, P  < 0.01), despite the high-fat meal providing 79.2 g more fat than the low-fat meal. It should also be mentioned that fat is more effectively absorbed from the gastrointestinal tract in comparison to carbohydrate. Lammert et al. ⁵¹ showed that a high-fat diet produced significantly lower fecal loss of energy than a high-carbohydrate diet. In addition, fat is known to improve the taste and texture of many food products, which may also promote active overconsumption associated with enhanced appetite due to sensory stimulation. ⁵² Increased food intake occurring with increased food palatability has been observed in many previous studies. ^53,–56 However, other studies that investigated the sensory properties of food involved in sensory-specific satiety found that increased sensory stimulation may reduce food consumption. ⁵⁷

A diet high in fat, particularly one rich in SFAs, may not only lead to a higher risk of obesity development, it may also have other adverse health effects. Generally, SFAs increase total and HDL-C levels, although not all SFAs affect plasma lipid and lipoprotein concentrations in the same manner. ⁵⁸ For example, stearic acid, in comparison with other SFAs, has little effect on plasma lipids; this has been proposed to be a result of the rapid conversion of stearic acid in the body to oleic acid. ⁵⁹ On the other hand, SFAs with 12–16 carbon atoms are considered to be hypercholesterolemic, and lauric acid (C12:0) appears to be more potent than myristic acid (C14:0) or palmitic acid (C16:0). ⁵⁹ However, it has been found that despite increasing serum total and LDL-C levels, C12:0, C14:0, and C16:0 acids also increase the concentration of HDL-C; as a result, they do not increase the ratio of total cholesterol to HDL-C. ⁶⁰ Whether a diet high in SFAs is associated with an increased risk of coronary heart disease is still controversial. ^60,61 A number of epidemiological and dietary intervention studies have found that a diet rich in SFAs is associated with a higher risk of impaired glucose tolerance, insulin resistance, and type 2 diabetes, ^62,–64 but there is no evidence of a direct causal relationship with CVD. ⁶⁵ Thanopoulou et al., ⁶² in a multinational survey, found that participants with recently diagnosed and undiagnosed type 2 diabetes had higher intakes of SFAs compared with healthy controls. These findings were similar to those of Wang et al. ⁶⁴ who, in a 9-year follow-up study of 2,909 American participants (45–64 years of age), showed a positive association between diabetes incidence and the proportion of total SFAs in plasma cholesterol esters and phospholipids, which reflects dietary intake of fatty acids. In addition, higher intake of SFAs may increase the risk of several cancers. Kurahashi et al. ⁶⁶ in a 7.5-year follow-up study among 43,435 Japanese men aged 45–74 years found that myristic and palmitic acids increased the risk of prostate cancer in a dose-dependent manner. Multivariable relative risk on comparison of the highest with the lowest quartiles of myristic acid and palmitic acid intake were 1.62 (1.15–2.29) and 1.53 (1.07–2.20), respectively. There is also evidence suggesting a possible relationship between SFA intake and a modest increase in breast cancer risk. ⁶⁷

One of the main sources of SFAs in takeaway or fast foods worldwide is palm oil, which is widely used as a frying medium due to excellent frying performance together with production of a highly desirable fried food flavor; it is especially popular in Southeast Asian countries, as well as in small, independent takeaway outlets in the United Kingdom. ^68,69 Palm oil is suggested as an acceptable alternative to PHVO in the deep fat frying process, but unhydrogenated vegetable oils are recommended as they produce a much more favorable plasma/serum lipid profile than either palm oil or partially hydrogenated oils. ⁵⁹ , ⁷⁰ In a dietary intervention study by Vega-López et al., ⁷⁰ 15 participants were provided for 5 weeks with food varying in the type of fat (partially hydrogenated soybean oil, soybean oil, palm oil, or canola oil; at two-thirds of total fat, or 20% of total energy). It was found that both partially hydrogenated soybean and palm oil resulted in higher LDL-C concentrations than other investigated fats. No significant differences in the total cholesterol to HDL-C ratio were observed among the diets enriched with palm, canola, and soybean oils. Vessby et al., ⁷¹ in the KANWU study, included 162 healthy participants who received an isoenergetic diet for 3 months containing either a high proportion of saturated or monounsaturated fatty acids, and found that replacement of SFAs with monounsaturated fatty acids was associated with improved insulin sensitivity.

On average, food eaten out of the home is characterized by a high total fat and SFA content. Stender et al., ⁷² after analyzing meals containing french fries and fried chicken (nuggets or hot wings) purchased from McDonald's and KFC outlets in 35 countries worldwide, found that the total fat content varied from 41 to 74 g depending on the country. These results were supported by later findings of Dunford et al., ⁷³ who reported that food items (burgers, chicken products, sides, or pizzas) purchased from fast-food chains contained between 10 and 13 g of total fat and between 3.9 and 4.9 g of SFAs per 100 g.

The intake of fat and SFAs increases along with higher frequency of out-of-home eating. ¹³ , ¹⁹ , ²¹ A study involving a large sample ( n  = 44,072) of adult African American women showed that total fat intake was significantly higher among women who reported eating out of the home at least once a week, regardless of the type of meals consumed (burgers, fried chicken, fried fish, Chinese food, pizzas, or Mexican food) when compared to those who had never eaten food prepared outside the home. ²¹ This is consistent with previous findings of Paeratakul et al., ¹³ which indicated that, among 9,063 adults and 8,307 children and adolescents, on the day when fast food was eaten, the intake of total fat, SFAs, and percentage of energy provided by fat was higher compared to the day without fast food consumption.

Trans Fatty Acids

Trans fatty acids are formed during the commercial partial hydrogenation of unsaturated fats. Small amounts of TFAs are also produced by ruminants during the biohydrogenation of unsaturated fatty acids from feed by hydrogen produced during the oxidation of substrates with bacterial enzymes in the rumen. These two sources of TFAs contain similar species of TFA isomers, but in different amounts and proportions; thus, their consumption may have different biological effects. ⁷⁴ The concentration of TFAs in partially hydrogenated vegetable oils (PHVO) may be as high as 30–50%, compared with only around 5% in dairy and ruminant meat products. ⁷⁴ Ruminant and industrially produced TFAs have been shown to have a detrimental effect on blood lipids when consumed in high doses; however, moderate intakes of ruminant TFAs, such as those seen with normal dietary consumption, have neutral effects on plasma lipids and other risk factors for cardiovascular disease. ⁷⁵ Hulshof et al. ⁷⁶ reported that TFA intake from ruminant products was under 2 g/day (<1% of total energy intake) in all Western European countries investigated in the TRANSFAIR study, and the main source of TFAs in the diet was PHVO. A more recent study estimated that average US consumption of industrially produced TFAs has significantly decreased from 4.6 g/per day (2003) to 1.3 g/per day (2010) as a result of food labelling and legislation. ⁷⁷ However, individuals with certain dietary habits may still consume high levels of industrially produced TFAs. ⁷⁷ Indeed, very high TFA intake levels (3.5–12.5% of total energy intake) have been shown in males aged 12–19 years, and the types of foods consumed included fast food such as french fries, pies, and pastries. ⁷⁸ In the United Kingdom, the National Diet Nutrition Survey reported an intake of less than 2 g per day of TFA, ⁷⁹ but this survey did not assess intake from takeaway food from independent outlets.

Trans fatty acids, due to their physiological effects, are undesirable components of the diet. A growing body of evidence has demonstrated numerous adverse effects associated with consumption of TFAs, including systemic inflammation, diabetes, insulin resistance, endothelial dysfunction, obesity, decreased LDL particle size, decreased HDL-C and apolipoprotein A1 concentrations, and increased total cholesterol, lipoprotein (a) and apolipoprotein B levels. ^80,81 A recent meta-analysis of the effects of TFA consumption on blood lipids and lipoproteins showed that each 1% energy replacement of TFAs with SFAs, monounsaturated fatty acids, or polyunsaturated fatty acids, respectively, decreased total cholesterol/HDL-C ratio by 0.31, 0.54, and 0.67; apolipoprotein B/apolipoprotein A1 ratio by 0.007, 0.010, and 0.011; and Lp(a) concentration by 3.76, 1.39, and 1.11 mg/L. ⁸² Esmaillzadeh et al. ⁸³ in a cross-sectional study of 486 apparently healthy women aged 40–60 years found that greater consumption of PHVO was associated with increased circulating concentrations of several markers of endothelial dysfunction and systemic inflammation. C-reactive protein, interleukin 6, and soluble tumor necrosis factor 2 levels were, respectively, 73%, 17%, and 5% higher among women in the highest quintile of TFA intake compared with the lowest quintile. ⁸⁴ Many studies that investigated an association between habitual intakes of or exposure to TFAs, assessed using tissue biomarkers (for example, erythrocyte membrane TFA concentrations, serum phospholipids, and adipose tissue fatty acid composition) have demonstrated a significantly increased risk of coronary heart disease among individuals with greater TFA consumption or exposure. ⁸⁵ The majority of these studies have focused on PHVO and, until recently, no positive association between ruminant TFA consumption and cardiovascular risk was found ⁸⁶ ; however, a recent study by Laake et al. ⁸⁷ found ruminant TFAs increased this risk, including for coronary heart disease, among women but not among men. Furthermore, TFA consumption may be associated with weight gain and visceral fat accumulation. A large prospective study conducted among 16,587 men, after controlling for potential confounders, found that substitution of each 2% of energy intake from TFAs by energy from polyunsaturated fatty acids was independently associated with a 2.7 cm increase in waist circumference over 9 years. ⁸⁸ It should also be mentioned that TFAs are transferred from the mother to the fetus across the placenta and are present in breast milk. ⁸⁰ , ⁸⁹ Because humans do not synthesize TFA isomers, the concentration of these isomers in human milk is directly related to the maternal diet. The content of TFAs in human milk varies among countries, from 0.5% in Africa, through 1.40–2.80% in Poland, to 6–7% of total fatty acids in Canada. ⁹⁰ A recent cross-sectional study found that infants of mothers who consumed 4.5 g or more of TFAs daily while breastfeeding were over two times more likely to have body fat higher than 24% in comparison to the offspring of mothers consuming less TFAs. ⁹¹

Takeaway and fast food, particularly french fries and deep-fried meats may contain a large amount of TFAs from PHVO, which are used for deep frying. It has been reported that a single meal of french fries (171 g) and fried chicken (160 g) purchased from fast food outlets provided from 0.3 to 24 g of TFAs. ⁷² Similarly, Wagner et al. ⁹² found that the TFA content in burgers may vary between 0.1 and 1.05 g per 100 g and in french fries between 0.1 and 1.6 g per 100 g. This is in agreement with Australian data reporting that the level of TFAs in takeaway meals may be between 0.1 and 1.4 g/100 g depending on the type of meal. ⁹³ Also, recent data from the United States showed that the content of TFAs in 32 representative fast-food samples ranged from 0.1 to 3.1 g per serving. ⁹⁴

It has been assessed that individuals who frequently consume fast-food meals could be receiving between 6 and 12% of their dietary energy from TFAs, ⁹⁵ and a single meal of fried chicken with chips may deliver four times more TFAs than the daily recommended allowance in the United Kingdom (i.e., no more than 2% of total recommended daily energy intake). ⁹⁶

In New York City, legal requirements regarding the use of PHVO in the preparation of foods sold by chain and nonchain restaurants have been implemented. Phase one of the initiative (2007) obligated all food outlets to use oils, shortenings, and margarines containing less than 0.5 g of TFAs per serving. Phase two (2008) involved reformulating all food items to contain less than 0.5 g of TFAs per serving. These restrictions have resulted in significant decreases in the TFA content of foods purchased, and between 2007 and 2009, the mean TFA content per purchase decreased by 2.4 g. However, the existing regulations in New York City apply only to restaurants that are required to hold a permit from the New York City Health Department ⁹⁷ ; thus, the level of TFAs in food products from independent outlets may be higher. ⁹⁸

It should be pointed out that most of the accessible studies regarding TFA levels in fast foods or other takeaway fried meal options did not distinguish between naturally occurring TFAs in food products and TFAs from PHVO, or they evaluated the levels of specific species of TFA isomers.

Conclusion

In summary, a growing body of evidence suggests that, even though positive changes are being made to improve the nutrient profiles of takeaway and fast foods, ⁷⁷ some of these frequently consumed foods may contribute to a variety of negative health outcomes, including cardiovascular disease, insulin resistance, type 2 diabetes, and obesity. ¹² , ^18,–22 Simultaneously, food prepared outside of the home is making up an increasing portion of the Western diet and there is no expectation that this trend will reverse or stop. However, most of the studies performed to date have only investigated the nutritional quality of food from fast-food restaurant chains, and there is still a lack of data regarding the nutrient content in takeaway meals from small independent outlets, including those serving such foods as ethnic cuisines, deli foods, fish and chips, and pizza. Furthermore, there is a lack of good-quality data on the consumption of different takeaway food options. To the best of our knowledge, no studies published to date have differentiated between consumption of fast foods and other types of takeaway meals, and the majority of previous studies have concentrated on foods from fast-food chain restaurants or have investigated food prepared outside of the home without considering the source, i.e., fast-food chain restaurants or independent takeaway outlets. However, recent work indicates there are significant differences in the nutrient composition of different types of takeaway meals (e.g., Indian, Chinese, English, pizzas, kebabs) ^99,100 as well as between takeaway meals and ready-to-eat meal options of a similar type. ^101,102 To date, only one study has examined the relationship between the frequency of consumption of specific types of meals eaten out of the home (i.e., burgers, pizzas, fried chicken, fried fish, Chinese food, and Mexican food) and the incidence of type 2 diabetes, but this study was limited to restaurant food only. ²¹ Furthermore, most studies have only investigated the frequency of out-of-home eating and have not taken into account the amount of food consumed, the overall diet quality, and other lifestyle factors. Therefore, more studies should be directed at furthering understanding of the nutrition and health consequences of both takeaway and fast food consumption and to finding the best strategies to reduce any negative impact their consumption may have on public health. Such strategies may require governmental regulation. In Finland, for example, legislation on food labelling, such as the mandatory warning of “high salt product” on products in which the salt concentration exceeds set limits, has been shown to be a useful tool to reduce salt intake in the population. ¹⁰³ Similarly, in Denmark, the restriction of industrially produced TFA levels of all food products to a maximum of 2% of the total fat content showed it is possible to reduce or remove TFAs from the content of food products. ¹⁰⁴

The cooperation of food technologists, nutritionists, and chefs is needed in order to alter the food preparation processes at fast-food and takeaway outlets with the goal of improving the nutritional quality of prepared meals. However, this may not be easy to achieve, as chefs and other decision makers may be reluctant to change recipes, especially due to concerns about adverse effects on palatability, which can potentially affect profits. Furthermore, voluntary guidelines do not always result in adequate changes to the nutritional quality of takeaway foods; thus, governmental regulations may be a more powerful means of effecting change.

Declaration of interest

The authors have no relevant interests to declare.

References