Association between home food preparation skills and behaviour, and consumption of ultra-processed foods: Cross-sectional analysis of the UK National Diet and nutrition survey (2008–2009)
© The Author(s). 2017
Received: 1 December 2016
Accepted: 11 May 2017
Published: 23 May 2017
‘Ultra-processed foods’ (UPF) have been industrially processed and tend to be higher in saturated fat, sodium and sugar than other foods. There is some evidence that consumption of UPF is associated with overweight, obesity and related diseases. In developed countries more than half of dietary energy is attributed to UPF. One reason for reliance on UPF may be poor home food preparation skills or infrequent use of these. This relationship has been previously proposed but not tested. We examined the relationship between home food preparation skills and behaviour and consumption of UPF.
We used data from adults in the UK National Diet & Nutrition Survey 2008–09. Home food preparation skills and behaviours of adults (n = 509) were assessed using questions on confidence using eight cooking techniques, confidence cooking 10 foods, ability to prepare a cake or biscuits without help, and whether or not participants prepared a main meal five or more days per week. Individuals’ UPF consumption was determined from four-day estimated diet diaries. Associations were adjusted for age, gender, occupational social class and household composition.
In fully adjusted models, individuals who were confident with all 10 foods (adjusted beta (95% CI) = −3.76 (−6.02 to −1.50)), able to bake cakes or biscuits without help (−3.87 (−6.62 to −1.12)), and cooked a main meal at least five days a week (−2.84 (−5.43 to −0.24)) consumed a lower percentage of dietary energy from UPF.
In UK adults better home food preparation skills and more frequent use of these skills tended to be cross-sectionally associated with lower UPF consumption. Greater encouragement of these skills may help reduce reliance on UPF.
‘Ultra-processed foods’ (UPF) are foods that have been industrially processed.  These foods tend to be higher in saturated fat, sodium and sugar than other foods. [2–6] Diets high in UPF tend to be lower in fruit and vegetables and fibre; and higher in sodium, saturated fat and sugar compared to diets lower in UPF. [2, 5, 7] Some, but not all, [2, 8] studies have reported positive associations between consumption of UPF and risk of overweight, obesity and markers of metabolic syndrome. [9–14].
Consumption of UPF varies internationally. In developed countries more than half of dietary energy has been attributed to UPF. [2, 3, 5, 6, 15, 16] Consumption is currently lower in less developed countries (where these foods are relatively less affordable ). [9, 18] Trends towards increasing consumption over time in less developed countries [10, 16, 19, 20] indicate that reliance on UPF may be a hallmark of the ‘nutrition transition’. .
Food classification based on the extent and purpose of industrial processing; from 
Group 1: Unprocessed or minimally processed foods
No processing or mostly physical processes used to make single whole foods more durable, accessible, convenient, palatable or safe
Fresh, chilled, frozen, vacuum-packed fruits, vegetables, fungi, roots and tubers; grains (cereals) in general; fresh, frozen and dried beans and other pulses (legumes); dried fruits and 100% unsweetened fruit juices; unsalted nuts and seeds; fresh, dried, chilled, frozen meats, poultry and fish; fresh and pasteurized milk, fermented milk such as plain yoghurt; eggs; teas, coffee, herb infusions, tap water, bottled spring water
Group 2: Processed ingredients
Extraction and purification of components of single whole foods, resulting in producing ingredients used in the preparation and cooking of dishes and meals made up from Group 1 foods in homes or traditional restaurants, or else in the formulation by manufacturers of Group 3 foods
Vegetable oils, margarine, butter, milk cream lard; sugar, sweeteners in general; salt; starches, flours, and “raw” pastas and noodles (made from flour with the addition only of water); and food industry ingredients usually not sold to consumers as such, including high fructose corn syrup, lactose, milk and soy proteins, gums, and preservatives and cosmetic additives
Group 3: Ultra-processed food products
Processing of a mix of Group 2 ingredients and Group 1 foodstuffs in order to create durable, accessible, convenient, and palatable ready-to-eat or to-heat food products liable to be consumed as snacks or desserts or to replace home-prepared dishes
Breads, biscuits (cookies), cakes and pastries; ice cream; jams (preserves); fruits canned in syrup; chocolates, confectionery (candies), cereal bars, breakfast cereals with added sugar; chips, crisps; sauces; savoury and sweet snack products; cheeses; sugared fruit and milk drinks and sugared and “no-cal” cola, and other soft drinks; frozen pasta and pizza dishes; pre-prepared meat, poultry, fish, vegetable and other “recipe” dishes; processed meat including chicken nuggets, hot dogs, sausages, burgers, fish sticks; canned or dehydrated soups, stews and pot noodle, salted, pickled, smoked or cured meat and fish; vegetables bottled or canned in brine, fish canned in oil; infant formulas, follow-on milks, baby food
Thus proposed reasons for increasing reliance on UPF include erosion of home food preparation skills and infrequent use of these skills. [23, 24] Adults in developed countries are spending less time on home food preparation, [25, 26] but there is little clear evidence for erosion of skills. For example, 89% of adults in the UK report being able to cook a main dish from basic ingredients. .
There is growing evidence that greater consumption of food prepared at home is associated with healthier diets.  However, as far as we are aware, no previous study has explored the relationship of home food preparation skills and behaviour with consumption of UPF in particular. We examined this relationship in UK adults. We hypothesised that those with better home food preparations skills and those who prepared food at home more frequently would consume a diet less reliant on UPF.
NDNS is an annual, cross-sectional survey collecting detailed dietary data and information on a range of other personal and household characteristics and food behaviours. In 2008–09 a series of questions on home food preparation skills and behaviours were included.
Household selection for NDNS takes place using multi-stage probability sampling. Firstly, a random sample of small geographical areas are selected to allow more efficient, geographically focused, data collection. Private addresses are then randomly selected within these areas from the Postcode Address File (a list of all addresses in the UK). If more than one household lives at a particular address, one is randomly selected for inclusion. Up to one adult (aged 19 years or older) and one child (aged 1.5–18 years) from each household is then randomly selected to take part. Households are first contacted by letter a few days before an interviewer visits. Data collection involves an in-person interview covering personal and household characteristics. In 2008–09 information on cooking skills and behaviours was also collected during this interview.
Following the interview an estimated four-day food diary with portion sizes based on common household measurements is then completed.  Dietary supplements were not included in our analyses. Those who completed three or four of the food diary days were thanked with shopping vouchers with a value of £30 (approx. €41.20, US$46.60). Data collection takes place throughout the year and diary days are selected to ensure balanced representation of all days of the week.
In 2008–09, NDNS reported that 89% (raw n not available) of households eligible for inclusion agreed to take part. Usable food diaries (three or four completed days) were collected from at least one person in 64% of eligible households. Overall 55% of those selected to take part completed usable diaries. .
All individuals aged at least 19 years at the time of participation, who completed three or four days of the food diary, and did not report any health problems limiting or preventing them from cooking were included in the analyses. Those younger than 19 years were excluded as they were not asked the questions on home food preparation skills and behaviour.
Variables of interest
Home food preparation skills and behaviour
Questions used to measure home food preparation skills and behaviours
Measure of home food preparation skills and behaviours
Confidence in using eight cooking techniques
Which, if any, of the following cooking techniques do you feel confident about using?
Boiling, steaming or poaching, frying, stir frying, grilling, oven-baking or roasting, stewing, braising, or casseroling, microwaving
Confidence in cooking ten foods
Which, if any, of the following foods do you feel confident about cooking?
Red meat, chicken, white fish (cod, haddock, plaice), oily fish (herring mackerel, salmon), pulses (such as split peas and lentils), dry pasta, rice (savoury), potatoes (not chips), green vegetables (cabbage, spinach, broccoli), root vegetables (carrots, parsnips)
Ability to prepare four different types of dish
Would you be able to make the following foods and dishes from beginning to end: convenience foods and ready meals (e.g. frozen pizza, pre-packaged curry & rice), a complete meal from ready-made ingredients (e.g. ready-made sauces and pasta to make spaghetti Bolognese), a main dish from basic ingredients (raw potatoes, raw meat, onions etc.), possibly following a recipe (e.g. shepherd’s pie, curry), a cake or biscuits from basic ingredients (flour, milk, eggs, etc.), possibly following a recipe
No, not at all, Yes, with a lot of help, Yes, with a little help, Yes, with no help at all
Frequency of preparing main meals
How often do you prepare a main meal for yourself or others?
Never, only for special occasions, less than once a week, one or two days a week, some days (3–4 a week), most days (5–6 a week), every day
Consumption of ultra-processed foods
Percentage of total energy intake obtained from UPF was calculated as previously.  In brief, firstly all foods in the NDNS nutrient databank were coded according to their degree of processing using the classification described in Table 1.  These codes were then merged with individual food diary data to determine the percentage of dietary energy each individual consumed from UPFs.
Co-variates included were gender, age, occupational social group, and household composition (measured in terms of whether or not other adults or children were present in the household). Occupational social group was measured using the National Statistics Socio-Economic Classification (NS-SEC) of the highest household earner. The full eight-level classification was collapsed into three groups for analysis: routine and manual, intermediate, or managerial and professional occupations.  Where no member of the household was currently employed classification was made based on the last main jobs of household members. These co-variates were chosen as there is evidence that they are associated with home food preparation skills and behaviour, [27, 33] and UPF consumption. [2, 15].
We used linear regression to explore associations between home food preparation skills and behaviour (‘exposure’ variables) and percentage of dietary energy from UPF (‘outcome’ variable). Separate models were run for each measure of home food preparation skills and behaviour (confidence with techniques, confidence with foods, ability to bake a cake or biscuits without help, and frequency of cooking). In all cases both unadjusted and fully adjusted (adjusted for sex, age, occupational social group, other adults in house, and children in household) models were run. As described above, all measures of home food preparation skills and behaviour were highly skewed and so were dichotomised in analyses. Throughout, age was entered as a continuous variable, occupational social class as an ordinal variable, and other adults and children in the household as binary variables.
A total of 548 adults aged 19 years or older completed three or four days of the NDNS food diary in 2008–09. Of these, 39 (7.1%) reported health problems limiting or preventing them from cooking. This left 509 meeting the inclusion criteria and included in the analysis. There were no other missing data.
Characteristics of individuals included in the analyses
n (%); (N = 509)
Age group (years)
Professional & managerial
Routine & manual
Participant lives with other adults
Participant lives with children
Home food preparation skills and behaviour
Confident with all 8 techniques
Confident will all 10 foods
Able to bake cake/biscuits without help
Cook main meal 5+ times per week
Unadjusted associations between individuals’ home food preparation skills and behaviours and percentage of dietary energy from ultra-processed foods (n = 509)*
Unadjusted regression coefficient (95% confidence intervals)
Confident with all 8 techniques (vs not)
−1.86 (−4.14 to 0.42)
Confident with all 10 foods (vs not)
−4.29 (−6.55 to −2.04)
Able to bake cake/biscuits without help (vs unable)
−2.49 (−5.05 to 0.07)
Cook main meal 5+ time per week (vs less often)
−2.70 (−5.14 to −0.26)
Adjusted associations between individuals’ home food preparation skills and behaviours and percentage of dietary energy from ultra-processed foods (n = 509)*
Adjusted regression coefficient (95% confidence intervals)
Confident with all 8 techniques
Confident with all 10 foods
Can bake cake or biscuits without help
Cook main meal 5+ time per week
Home food preparation skill or behaviour
−1.56 (−3.87 to 0.75)
−3.76 (−6.02 to −1.50)
−3.87 (−6.62 to −1.12)
−2.84 (−5.43 to −0.24)
1.31 (−0.99 to 3.62)
1.51 (−0.77 to 3.79)
2.71 (0.20 to 5.22)
2.09 (−0.36 to 4.53)
−0.16 (−0.24 to −0.09)
−0.16 (−0.23 to −0.09)
−0.17 (−0.24 to −0.09)
−0.16 (−0.23 to −0.09)
Other adults in household
0.45 (−2.07 to 2.97)
0.50 (−1.99 to 3.00)
0.46 (−2.05 to 2.97)
0.18 (02.35 to 2.70)
Children in household
0.54 (−2.18 to 3.26)
0.25 (−2.43 to 2.92)
0.64 (−2.05 to 3.33)
0.31 (−2.39 to 3.00)
NS-SEC (intermediate vs managerial & professional)
−1.05 (−4.11 to 2.02)
−1.20 (−4.24 to 1.84)
−1.25 (−4.30 to 1.80)
−0.83 (−3.89 to 2.23)
NS-SEC (routine & manual vs managerial & professional)
1.52 (−1.02 to 4.07)
1.06 (−1.46 to 3.59)
1.63 (−0.87 to 4.13)
1.85 (−0.63 to 4.35)
Summary of results
This is the first exploration of the association between home food preparation skills and behaviour, and consumption of UPF that we are aware of. In partial support of our hypothesis we found that some markers of individuals’ own home food preparation skills and behaviour were significantly associated with UPF consumption. Where associations were found, greater home food preparation skills or frequency was associated with lower consumption of UPF.
Interpretation of results
Where significant associations were present, we found that those who were more confident or prepared food more frequently consumed around 3–4 fewer percentage points of energy from UPF than others. With a mean daily energy intake in the sample of 7894 kJ (1887 kcal) (data not shown), this difference represents around 237–316 fewer kJ (57-75 kcal) from UPFs per day; or around 40–50% of a 330 ml can of regular Coca-cola. This difference is not insubstantial and reflects previous findings of relationships between both better home cooking skills and greater frequency of consuming home cooked food, and dietary quality. [28, 34].
Our results were not entirely consistent. Confidence with all eight techniques was not associated with consumption of UPF. Perhaps somewhat un-intuitively, it is possible that confidence with all eight techniques is the measure that is least related to practical use of home food preparation skills. For instance confidence with preparing a range of foods, being able to bake a cake or biscuits, and preparing a main meal frequently might all be expected to reflect individuals’ applied use of home food preparation skills. In contrast, confidence with all eight techniques may reflect more theoretical knowledge. Previous authors have highlighted the limitations of existing conceptualisations and measures of home cooking skills and behaviours.  Further work is required to develop valid and reliable measures of clear concepts. [36, 37].
The only other consistent correlate of individuals’ UPF consumption that we found was age. In all cases there was an inverse association with older individuals tending to consume a lower percentage of energy from UPF. Similar patterns have been previously described in relation to UPF consumption in particular,  and ‘healthier’ diets in general.  Further work will be required to determine if this a true age effect or a cohort effect.
Implications of results for research, policy and practice
Our finding that some, but not all, measures of home food preparation skills and behaviours are associated with UPF consumption reiterate the complexity of home food preparation.  Our analyses also highlight the poor current conceptualisation of what home food preparation skills and behaviours are,  what aspects of them matter for diet and health,  and the absence of valid and reliable measures of these skills and behaviours. [36, 37] Despite using the most comprehensive food and diet dataset currently available in the UK, these issues all limit the interpretations we can make. Researchers need to make progress on conceptualisation and operationalisation of home food preparation skills and behaviour, and how these may influence dietary quality and health as a matter of urgency.
Further research is also needed to confirm our results in longitudinal settings and so increase confidence that the associations reported here are causal. If this is confirmed our results suggest that providing individuals with practical home food preparation skills and encouraging them to use these on most days of the week may be one method to decrease consumption of UPFs.
Limitations of methods
Our study is cross-sectional and the associations reported should not be interpreted as causative. Further longitudinal research is necessary to determine the direction of any causation between home food preparation skills and behaviour and consumption of UPF.
Although NDNS invites a population-representative sample, the achieved sample is not necessarily representative due to selective non-response.  However, the sample included in our analysis represents the full diversity of the UK population in terms of age, gender and socio-economic characteristics meaning the associations we found are likely to be generalizable to the UK. Given international differences in food preparation and consumption behaviours [38, 39] our findings may not be more widely generalizable.
The data we used was entirely self-reported and may be subject to social desirability bias. Whilst food diaries are recognised to be one of the most comprehensive methods of assessing dietary intake,  selective under-reporting of some foods (particularly less healthy foods) occurs. [41, 42] The extent and nature of this may vary between population sub-groups. [41, 42] There may also be social pressures to over-report home food preparation skills and behaviour. Variations in interpretation of the questions used to assess home food preparation skills and behaviour may have introduced further error or bias. The provenance of the questions on home food preparation skills and behaviour is unclear and we are not aware of any published assessments of validity or reliability. There are few established, agreed and validated measures of cooking skills.  This is partly related to the poor conceptualisation of home cooking.  It is difficult to predict what the influence of these potential biases may have been on the results reported. Given how difficult it is to assess selective under-reporting, we did not correct for it.
The data used are now 7–8 years old and may not reflect the current situation in the UK. However, they are the most recent and comprehensive data from the UK we are aware of on this topic.
In UK adults, better home food preparation skills and more frequent use of these skills tended to be cross-sectionally associated with lower UPF consumption. Further work is required to conceptualise and operationalise home food preparation skills and behaviours. Greater encouragement of these skills may help reduce reliance on UPF.
Ethics approval and consent to participants
Ethical approval for NDNS in 2008–09 was provided by Oxfordshire A Research Ethics Committee. All participants provided written, informed consent to participate. Additional ethical approval for this analysis was not required.
This work was undertaken by the Centre for Diet and Activity Research (CEDAR), a UKCRC Public Health Research Centre of Excellence. Funding from the British Heart Foundation, Cancer Research UK, Economic and Social Research Council, Medical Research Council, the National Institute for Health Research, and the Wellcome Trust, under the auspices of the UK Clinical Research Collaboration, is gratefully acknowledged. The funders played no role in the design, conduct or interpretation of this research, or the decision to publish.
Availability of data and materials
Anonymised data and data collection materials were obtained from the UK Data Archive and is available to other eligible researchers directly from the Archive (http://dx.doi.org/10.5255/UKDA-SN-6533-6).
JA conceived the idea for this work. MCLL and JA developed the methods. MCLL conducted the analysis. MCLL and JA interpreted the data, drafted the manuscript and critically revised it. All authors read and approved the final manuscript.
The authors declare they have no competing interests.
Consent for publication
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