Open Access Article
Xuzhi
Wan
a,
Yang
Ao
b,
Xiaohui
Liu
b,
Pan
Zhuang
a,
Yingyu
Huang
a,
Hongbo
Shi
a,
Jingjing
Jiao
b and
Yu
Zhang
*a
aDepartment of Gastroenterology, The First Affiliated Hospital, Zhejiang University School of Medicine, Department of Food Science and Nutrition, Zhejiang Key Laboratory for Agro-Food Processing, College of Biosystems Engineering and Food Science, Zhejiang University, Hangzhou, Zhejiang, China. E-mail: y_zhang@zju.edu.cn; Tel: +86-571-88982211
bDepartment of Endocrinology, The Second Affiliated Hospital, Department of Nutrition, School of Public Health, Zhejiang University School of Medicine, Hangzhou, Zhejiang, China
First published on 31st January 2024
Background and aims: Genetic and dietary factors contribute to adiposity risk, but little evidence supports genetic personalization of fried food intake recommendations for the management of obesity. This study aimed to assess the associations between fried food consumption and adiposity incidence and whether the associations were modified by an individual's genotype. Methods: We included 27
427 participants who had dietary data assessed by a validated 24 h dietary recall and available anthropometric information from the UK Biobank study. The genetic risk score (GRS) was calculated using 940 BMI associated variants. Results: With an average of 8.1 years of follow-up, 1472 and 2893 participants were defined as having overall obesity and abdominal obesity, respectively. Individuals in the highest categories of fried food consumption were positively associated with the risk of obesity (HR = 1.31; 95% CI 1.10–1.56) and abdominal obesity (HR = 1.27; 95% CI 1.12–1.45) compared with the lowest categories. Moreover, fried food consumption had a significant interatction with obesity GRS for abdominal obesity risk (P interaction = 0.016). Fried food intake was associated with a higher abdominal obesity risk (HR = 1.59, 95% CI: 1.25–2.00) among participants with a lower genetic risk. Conclusions: Our findings indicated that fried food consumption had a higher abdominal obesity risk among individuals with a lower genetic risk, suggesting the restriction of fried food intake for this group of people.
The latest meta-analysis report states that fried food consumption increases obesity risk and subsequently leads to other cardiometabolic diseases.12 Recent epidemiological discoveries described significant and positive association of fried food intake with adiposity incidence in Europe.13,14 Such studies, however, used food frequency questionnaires to calculate the intake of specific fried food or total fried food, which are more subject to social desirability bias.15 Comparatively, a 24 h diet recall can reduce the impact of recall bias and better capture precise information of foods consumed, especially that of fried foods.16 In addition, previous studies failed to examine the influence of specific fried foods on adiposity risk due to the insufficient size of the population or incomplete dietary information.17 Thus, it is unclear whether different subtypes of fried foods confer divergent obesogenic effects.
Although dietary factors such as overeating have been thought to be a main cause of adiposity, an individual's genotype may interact with dietary components related to obesity development, also known as the gene–diet interaction.18,19 Despite previous studies indicating the effect of significant interactions between fried food and certain genetic variants on the body mass index (BMI),17 none of the interactions have been robustly replicated on obesity risk, which could be due to insufficient statistical data and limited genetic variants. Recent genome-wide association studies (GWAS) have identified 941 independent single-nucleotide polymorphisms (SNPs) associated with the BMI that determine genetic susceptibility to weight gain,20 which considerably increased the predictive ability for obesity by genetic factors. Unfortunately, little knowledge on whether the effect of fried food consumption on obesity development is modified by the overall genetic burden has been recognized.
To address these major gaps, we assessed the relationships between fried food consumption and incident adiposity, including overall and abdominal obesity among participants in the UK Biobank cohort. Furthermore, we tested the potential interaction of fried food consumption with genetic risk of adiposity.
Overall, 59
646 participants with available data on anthropometric data at baseline (2006 to 2010) and at least one of three repeated measurements (2012 to 2013, 2014 to date, and 2019 to date) during the follow-up were initially included. After excluding patients with cancer, cardiovascular diseases, or BMI ≥30 kg m−2 at baseline, individuals without 24 h-diet recall information, and participants who withdrew during the follow-up, 27
427 participants were selected to analyze the associations of fried food consumption with incident obesity. To further assess the potential interaction of fried food intake with the genetic predisposition to obesity, we excluded individuals without genetic data and not of white British descent. Finally, a total of 26
250 participants were eligible for the gene–diet interaction assessment (ESI Fig. S1†).
,22 where β is the coefficient for each individual SNP and i is the number of risk allele of SNPs. The overall GRS ranged between 801.7 and 971.4. The individuals with a higher GRS were suggested to have a higher genetic predisposition of obesity.
We constructed a diet quality score based on the Alternate Mediterranean Diet (AMED) ranging from 0 to 9 as previously described, while a higher score indicated a higher quality of diet (ESI Table S2†).24 Furthermore, potential confounders were collected by using the touch screen questionnaire, including age, sex, ethnicity, BMI, average household income, education, Townsend deprivation index, physical activity, smoking, alcohol drinking, disease history, medications and dietary supplements. The metabolic equivalent of task (MET) was calculated by using the International Physical Activity Questionnaire short form.24 A detailed description of these covariates has been provided elsewhere (https://www.ukbiobank.ac.uk). The sleep pattern was classified as described in a previous study.25
We then conducted subgroup analyses to examine whether these associations varied by typical baseline characteristics. In sensitivity analyses, history of hypertension or diabetes, vitamin or mineral supplement, sedentary time, and the changes in lifestyle factors during the follow-up were further adjusted in the models. Second, we further excluded participants with a BMI ≤15 kg m−2, extreme energy intake (<500 or >3500 kcal d−1 for women and <800 or >4000 kcal d−1 for men),27 missing covariate data, or with cardiometabolic diseases during the follow-up.
All analyses were performed using SAS 9.4 software (SAS Institute, Cary, NC). A two-tailed P < 0.05 was defined as statistically significant.
250) was 889.6 with a normal distribution (ESI Fig. S2†).
| Characteristics | Fried food consumption (servings per day) | P value* | |||
|---|---|---|---|---|---|
| 0 | 0–1 | 1–1.5 | ≥1.5 | ||
| BMI = body mass index, MET = metabolic equivalent, SBP = systolic blood pressure, DBP = diastolic blood pressure. Data are either percentages or means ± SDs unless indicated otherwise. *P value for continuous variables was estimated through unadjusted linear regression, treating quintile of fried food consumption as an ordinal variable, and Pearson's χ2 for categorical variables.a £1.00 = $1.30, or €1.20.b The Townsend deprivation index was an indicator of material deprivation that was calculated based on non-home ownership, non-car ownership, unemployment, and household over-crowding. | |||||
| N | 10 232 |
10 408 |
4191 | 2596 | |
| Male (%) | 42.8 | 46.0 | 53.0 | 57.6 | <0.001 |
| Race (%) | 0.002 | ||||
| White | 97.1 | 97.5 | 96.9 | 96.0 | |
| Non-white | 2.7 | 2.2 | 2.8 | 3.7 | |
| Age (year) | 55.8 ± 7.4 | 55.6 ± 7.5 | 54.3 ± 7.7 | 53.2 ± 7.8 | <0.001 |
| BMI (kg m−2) | 24.9 ± 2.7 | 25.0 ± 2.7 | 25.2 ± 2.6 | 25.4 ± 2.6 | <0.001 |
| Physical activity (MET-h per wk) | 42.0 ± 38.9 | 40.2 ± 37.6 | 41.6 ± 40.1 | 42.0 ± 42.0 | 0.118 |
| SBP (mmHg) | 136.6 ± 19.2 | 136.9 ± 19.1 | 136.1 ± 18.3 | 135.8 ± 18.4 | 0.030 |
| DBP (mmHg) | 80.2 ± 10.3 | 80.6 ± 10.3 | 80.8 ± 10.6 | 80.8 ± 10.5 | <0.001 |
| Blood glucose (mmol L−1) | 5.0 ± 0.9 | 5.0 ± 0.8 | 4.9 ± 0.9 | 4.9 ± 0.9 | 0.111 |
| Household income (£) (%)a | <0.001 | ||||
<18 000 |
10.4 | 9.8 | 9.0 | 9.4 | |
18 000 to 30 999 |
20.1 | 21.0 | 20.6 | 18.3 | |
31 000 to 51 999 |
27.4 | 27.2 | 28.9 | 30.7 | |
52 000 to 100 000 |
26.3 | 26.5 | 26.8 | 27.8 | |
>100 000 |
7.7 | 8.0 | 6.9 | 6.5 | |
| Education | <0.001 | ||||
| College or University degree | 52.9 | 53.6 | 47.4 | 47.0 | |
| Vocational qualifications | 8.9 | 9.3 | 10.0 | 10.5 | |
| Optional national exams at age 17–18 years | 13.1 | 13.4 | 13.6 | 12.9 | |
| National exams at age 16 years | 20.2 | 19.4 | 23.3 | 24.8 | |
| Others | 4.7 | 4.1 | 5.5 | 4.6 | |
| Townsend deprivation indexb | −2.0 ± 2.7 | −2.1 ± 2.6 | −2.0 ± 2.7 | −1.9 ± 2.7 | 0.198 |
| Smoking (%) | <0.001 | ||||
| Never | 63.7 | 62.8 | 59.6 | 60.0 | |
| Previous | 30.8 | 31.7 | 33.2 | 31.9 | |
| Current | 5.4 | 5.3 | 6.9 | 7.9 | |
| Alcohol drinking (%) | <0.001 | ||||
| Never or special occasions only | 23.1 | 20.9 | 21.2 | 21.6 | |
| 1 to 3 times per month | 25.2 | 24.5 | 25.2 | 24.9 | |
| 1 or 2 times per week | 29.2 | 29.4 | 29.9 | 29.1 | |
| 3 or 4 times per week | 22.5 | 25.2 | 23.6 | 24.4 | |
| Sleep pattern | <0.001 | ||||
| Poor | 4.0 | 3.3 | 4.2 | 5.2 | |
| Intermediate | 56.5 | 56.5 | 57.0 | 58.6 | |
| Healthy | 39.4 | 40.1 | 38.8 | 36.2 | |
| History of hypertension (%) | 45.7 | 46.8 | 44.5 | 44.3 | 0.016 |
| History of high cholesterol (%) | 2.1 | 1.9 | 2.0 | 2.2 | 0.018 |
| Mediterranean Diet Score | 3.9 ± 1.9 | 4.3 ± 1.8 | 3.7 ± 1.8 | 3.8 ± 1.8 | <0.001 |
| Energy intake (kcal) | 8359.4 ± 2446.3 | 8906.5 ± 2177.0 | 9594.2 ± 2515.0 | 10 559.0 ± 2974.4 |
<0.001 |
| Vitamin use (%) | 32.9 | 30.9 | 31.7 | 30.6 | 0.008 |
| Mineral use (%) | 14.3 | 12.9 | 11.2 | 10.7 | <0.001 |
158 person-years of follow-up (an average of 8.1 years), we documented 1472 and 2893 cases of obesity and abdominal obesity, respectively. In Model 1, fried food consumption was significantly and positively associated with incident obesity and abdominal obesity (Table 2). After further adjustment for lifestyle factors (Model 2), the HRs (95% CIs) comparing the highest frequent consumption of fried food (≥1.5 servings per day) with non-consumption were 1.41 (1.19–1.67) and 1.38 (1.21–1.57) for the risk of obesity and abdominal obesity, respectively. The HRs (95% CIs) across increasing categories of fried food were 1.10 (0.97–1.25), 1.06 (0.91–1.24), and 1.31 (1.10–1.56) for obesity risk and 1.09 (1.00–1.19), 1.06 (0.95–1.19) and 1.27 (1.12–1.45) for abdominal obesity risk in the fully adjusted models (Model 3), respectively. Each SD increment in fried food consumption was related to a 6% (1%–11%) higher obesity risk and a 5% (2%–9%) higher abdominal obesity risk. For different specific food groups, compared with the first categories, consumers in the highest categories of fried potato had a 45% higher risk of incident obesity and a 49% higher risk of abdominal obesity (ESI Table S4†). Nonetheless, non-significant associations were detected for fried white meat consumption (ESI Table S5†). The dose–response relationships for fried food consumption determined by the restricted-cubic-spline regression were all similar to those from the category analyses (Fig. 1).
| Fried food intake (servings per day) | P-trenda | Per 1-SD | P value | ||||
|---|---|---|---|---|---|---|---|
| 0 | 0–1 | 1–1.5 | ≥1.5 | ||||
BMI = body mass index, WC = waist circumference, BF = body fat, HRs = hazard ratios, CIs = confidence intervals. Cox proportional hazards regression analyses were used to calculate the HRs and 95% CIs.a P-trend was obtained by including the categories of fried food intake as a continuous variable in the model.b Model 1 was adjusted for age (continues) and sex (male or female).c Model 2 was further adjusted for race (White or non-White), centers (22 categories), education (college or university degree, vocational qualifications, optional national exams at age 17–18 years, national exams at age 16 years, others, or missing), Townsend deprivation index (quartiles), household income (<£18 000, £18 000–£30 999, £31 000–£51 999, £52 000–£100 000, >£100 000, or missing), smoking (never, former, current, or missing), alcohol consumption (never or special occasions only, 1 or 2 times per week, 3 or 4 times per week, ≥5 times per week, or missing), physical activity (quartiles), sleep pattern (poor, medium or healthy), Mediterranean diet score (quartiles), and energy intake (quartiles).d Model 3 was further adjusted for baseline BMI (in kg m−2; <18.5, 18.5 to 25, or 25 to 30) for obesity or adjusted for the baseline BMI (in kg m−2; <18.5, 18.5 to 25, or 25 to 30) and WC (quartiles) for abdominal obesity.e Excluding 3 participants without data of WC at baseline or follow-up duration.f Excluding 710 participants without data of BF% at baseline or follow-up duration. |
|||||||
| N | 10 232 |
10 408 |
4191 | 2596 | |||
| Obesity case | 499 | 527 | 244 | 202 | |||
| Model 1b | 1.00 (Ref.) | 1.09 (0.96–1.23) | 1.19 (1.02–1.38) | 1.59 (1.35–1.87) | <0.001 | 1.12 (1.07–1.16) | <0.001 |
| Model 2c | 1.00 (Ref.) | 1.15 (1.02–1.30) | 1.15 (0.98–1.34) | 1.41 (1.19–1.67) | <0.001 | 1.08 (1.03–1.12) | <0.001 |
| Model 3d | 1.00 (Ref.) | 1.10 (0.97–1.25) | 1.06 (0.91–1.24) | 1.31 (1.10–1.56) | 0.009 | 1.06 (1.01–1.11) | 0.018 |
| Abdominal obesity case | 1019 | 1074 | 467 | 333 | |||
| Model 1b | 1.00 (Ref.) | 1.14 (1.04–1.24) | 1.26 (1.13–1.41) | 1.58 (1.39–1.79) | <0.001 | 1.13 (1.09–1.16) | <0.001 |
| Model 2c | 1.00 (Ref.) | 1.16 (1.06–1.26) | 1.17 (1.04–1.30) | 1.38 (1.21–1.57) | <0.001 | 1.09 (1.05–1.12) | <0.001 |
| Model 3d | 1.00 (Ref.) | 1.09 (1.00–1.19) | 1.06 (0.95–1.19) | 1.27 (1.12–1.45) | 0.002 | 1.05 (1.02–1.09) | 0.007 |
| Case having a ≥5% BMI increase | 1925 | 1946 | 884 | 629 | |||
| Model 1b | 1.00 (Ref.) | 1.04 (0.98–1.11) | 1.13 (1.04–1.22) | 1.34 (1.23–1.47) | <0.001 | 1.08 (1.05–1.10) | <0.001 |
| Model 2c | 1.00 (Ref.) | 1.06 (1.00–1.13) | 1.08 (1.00–1.18) | 1.22 (1.11–1.35) | <0.001 | 1.05 (1.02–1.07) | <0.001 |
| Model 3d | 1.00 (Ref.) | 1.06 (1.00–1.13) | 1.09 (1.00–1.18) | 1.23 (1.12–1.35) | <0.001 | 1.05 (1.02–1.07) | <0.001 |
| Case having a ≥5% WC increase | 3357 | 3326 | 1420 | 898 | |||
| Model 1b | 1.00 (Ref.) | 1.04 (0.99–1.09) | 1.09 (1.03–1.16) | 1.18 (1.09–1.27) | <0.001 | 1.05 (1.03–1.07) | <0.001 |
| Model 2c | 1.00 (Ref.) | 1.05 (1.00–1.11) | 1.04 (0.98–1.11) | 1.10 (1.02–1.19) | 0.014 | 1.02 (1.00–1.04) | 0.055 |
| Model 3d | 1.00 (Ref.) | 1.08 (1.03–1.13) | 1.08 (1.01–1.15) | 1.15 (1.07–1.25) | <0.001 | 1.04 (1.01–1.06) | 0.003 |
| Case having a ≥ 5% BF% increase | 4740 | 4903 | 2080 | 1364 | |||
| Model 1b | 1.00 (Ref.) | 1.07 (1.03–1.11) | 1.06 (1.01–1.12) | 1.13 (1.06–1.20) | <0.001 | 1.03 (1.01–1.04) | 0.002 |
| Model 2c | 1.00 (Ref.) | 1.07 (1.03–1.11) | 1.02 (0.96–1.07) | 1.05 (0.99–1.12) | 0.154 | 1.01 (0.99–1.02) | 0.172 |
| Model 3d | 1.00 (Ref.) | 1.09 (1.05–1.14) | 1.05 (0.99–1.10) | 1.09 (1.03–1.16) | 0.004 | 1.01 (1.00–1.03) | 0.113 |
For adiposity indicators, we detected a positive association between fried food intake and participants having more than a 5% increase of the BMI (HRC4 vs. C1: 1.23, 95% CI: 1.12–1.35), WC (HRC4 vs. C1: 1.15, 95% CI: 1.07–1.25), and BF% (HRC4 vs. C1: 1.09, 95% CI: 1.03–1.16) in the fully adjusted model (Model 3) (Table 2). We also observed that fried potato consumption was positively associated with a higher risk for the BMI and BF% increase (ESI Table S4†). However, fried white meat consumption was not significantly associated with these adiposity indicators (ESI Table S5†).
GRS (n Loci = 940) |
|||||||||
|---|---|---|---|---|---|---|---|---|---|
| Diet | GRS | Diet × GRS | |||||||
| β* | SE | P | β* | SE | P | β* | SE | P | |
BMI = body mass index, WC = waist circumference, BF = body fat, GRS = genetic risk score. Cox proportional hazards regression analyses were used to calculate the HRs and 95% CIs. The model was adjusted for age (continuous), sex (male or female), race (White or non-White), centers (22 categories), education (college or university degree, vocational qualifications, optional national exams at age 17–18 years, national exams at age 16 years, others, or missing), Townsend deprivation index (quartiles), household income (<£18 000, £18 000–£30 999, £31 000–£51 999, £52 000–£100 000, >£100 000, or missing), smoking (never, former, current, or missing), alcohol consumption (never or special occasions only, 1 or 2 times per week, 3 or 4 times per week, ≥5 times per week, or missing), physical activity (quartiles), sleep pattern (poor, medium or healthy), Mediterranean diet score (quartiles), and energy intake (quartiles). The model was adjusted for age (continuous), sex (male or female), race (White or non-White), centers (22 categories), education (college or university degree, vocational qualifications, optional national exams at age 17–18 years, national exams at age 16 years, others, or missing), Townsend deprivation index (quartiles), household income (<£18 000, £18 000–£30 999, £31 000–£51 999, £52 000–£100 000, >£100 000, or missing), smoking (never, former, current, or missing), alcohol consumption (never or special occasions only, 1 or 2 times per week, 3 or 4 times per week, ≥5 times per week, or missing), physical activity (quartiles), sleep pattern (poor, medium, healthy), Mediterranean diet score (quartiles), energy intake (quartiles), and baseline BMI (in kg m−2; <18.5, 18.5 to 25 or 25 to 30) for obesity or adjusted for the baseline BMI (in kg m−2; <18.5, 18.5 to 25 or 25 to 30) and WC (quartiles) for abdominal obesity.a Excluding 3 participants without data of WC at baseline or follow-up duration.b Excluding 710 participants without data of BF% at baseline or follow-up duration. |
|||||||||
| Fried food | |||||||||
| Obesity | 0.070 | 0.025 | 0.005 | 0.156 | 0.027 | <0.001 | 0.009 | 0.023 | 0.693 |
| Abdominal obesity | 0.052 | 0.018 | 0.005 | 0.088 | 0.019 | <0.001 | −0.039 | 0.016 | 0.016 |
| BMI increase | 0.103 | 0.014 | <0.001 | 0.164 | 0.013 | <0.001 | 0.012 | 0.012 | 0.337 |
| WC increasea | 0.265 | 0.044 | <0.001 | 0.318 | 0.042 | <0.001 | 0.017 | 0.040 | 0.664 |
| BF% increaseb | 0.181 | 0.025 | <0.001 | 0.151 | 0.024 | <0.001 | 0.004 | 0.023 | 0.855 |
| Fried potato | |||||||||
| Obesity | 0.062 | 0.025 | 0.012 | 0.158 | 0.028 | <0.001 | −0.002 | 0.022 | 0.918 |
| Abdominal obesity | 0.071 | 0.019 | <0.001 | 0.088 | 0.019 | <0.001 | −0.026 | 0.017 | 0.117 |
| BMI increase | 0.109 | 0.014 | <0.001 | 0.165 | 0.013 | <.0001 | −0.00001 | 0.013 | 1.000 |
| WC increasea | 0.288 | 0.045 | <0.001 | 0.320 | 0.042 | <0.001 | −0.011 | 0.042 | 0.783 |
| BF% increaseb | 0.214 | 0.026 | <0.001 | 0.153 | 0.024 | <0.001 | −0.005 | 0.024 | 0.839 |
| Fried white meat | |||||||||
| Obesity | 0.042 | 0.022 | 0.061 | 0.158 | 0.027 | <0.001 | 0.013 | 0.020 | 0.519 |
| Abdominal obesity | −0.006 | 0.020 | 0.749 | 0.086 | 0.019 | <0.001 | −0.017 | 0.016 | 0.288 |
| BMI increase | 0.015 | 0.013 | 0.255 | 0.164 | 0.013 | <0.001 | 0.005 | 0.011 | 0.679 |
| WC increasea | −0.020 | 0.043 | 0.637 | 0.319 | 0.042 | <0.001 | 0.0003 | 0.036 | 0.993 |
| BF% increaseb | 0.017 | 0.025 | 0.501 | 0.152 | 0.024 | <0.001 | 0.010 | 0.020 | 0.631 |
In category analyses, similar positive relationships were observed between fried food consumption and obesity risk across all genetic risk groups (Fig. 2A). Increased fried food was related to more increases in abdominal obesity among individuals with a low GRS risk (Fig. 2B). The HRs (95% CIs) of abdominal obesity risk across increasing categories of fried food were 0.99 (0.83–1.17), 1.17 (0.96–1.44), and 1.59 (1.25–2.00) in the fully adjusted model (P interaction = 0.015) (Fig. 2B). For the adiposity indicators, the consumption of fried food was positively associated with the BMI, WC, and BF% across all genetic risk groups (C4vs. C1: β = 0.74 for BMI, β = 1.78 for WC, β = 1.06 for BF%, all P < 0.001) (Fig. 3A–D).
In sensitivity analyses, the relationships between fried food intake and adiposity development did not change obviously after further adjustment for the history of hypertension or diabetes, the use of vitamin or mineral supplements, sedentary time, or changes in lifestyle factors (ESI Tables S6–S8†). Moreover, the results also appeared similar after excluding participants who developed cardiometabolic diseases during the follow-up, participants with an extremely low BMI (≤15 kg m−2) or extreme energy intake, or participants with missing covariate data (ESI Tables S6–S8†).
Since frying leads to the property of processed food with high fat and high energy density and thus links to the occurrence of adiposity,28 restricting fried food consumption is widely recommended to reduce obesity-related diseases.12 Few and inconsistent evidence has focused on the relationships between fried food consumption and obesity development in previous studies. A cross-sectional study has reported a 26% higher obesity risk with increased fried food intake among Spanish population.13 A previous twin cohort study based on the SUN project has also found that fried food intake had an increased obesity risk.14 However, we are simultaneously aware that a cross-sectional Korean study failed to detect a significant association of fried food consumption with obesity.29 These inconsistent results can partly be explained by differences in frying methods and foods in different countries. For example, fried meat was the most consumed fried food (45%), followed by vegetables (31%), fish (12%), and seaweed (8%) among Korean adults.29 High intake of healthy food with less energy such as vegetables among Korean population might attenuate the associations of fried food with obesity development.30 In the present study, we also found that fried potato but not fried white meat consumption was positively associated with obesity and abdominal obesity risk. This is in line with findings from a systematic review that increased consumption of French fries was related to a higher BMI and weight gain.31 The null associations between fried white meat intake and incident obesity may be attributed to diverse cooking methods and types of oil used.32 In the United Kingdom, fish or chicken is prepared in battered or breaded form, which might inhibit fat absorption and retain the quality attributes of fried fish or chicken.33 Evidence also showed that higher consumption of fish and marine n-3 PUFAs could reduce long-term weight gain.34 The high content of animal-sourced protein in chicken increases satiety, which may simultaneously attenuate energy intake.35 In addition, fried poultry and fish were usually cooked using butter that is rich in bone-building calcium, and the intake of these two fried foods was associated with a lower risk of obesity.36 Our findings, together with other previous studies,37 further highlighted the obesogenic role of fried food, especially fried potatoes, in developing adiposity risk.
Our current findings added to the existing literature on the interaction between genetic and dietary factors by assessing whether obesity-capturing GRS could interact with fried food on obesity risk. It is well-known that genetic factors modulate the associations between dietary factors and incident obesity.38 In terms of fried food, limited studies have examined the interplay between fried food intake and genetic susceptibility to BMI.17 In three US cohort studies, higher adherence to fried food consumption was related to an increased BMI among participants with a high GRS using 32 variants.17 However, the GRS captured by limited variants only reflects 1.5% of the variation in the BMI and might not precisely predict inherent risk for obesity.39 Our study used 940 BMI-associated SNPs based on the largest GWAS study, which could explain 6% of BMI variance20 and unprecedentedly enhance the accuracy of an individual's genetic risk on future development of adiposity. Our findings emphasized the synergistic genetic effect on abdominal obesity among individuals with a lower genetic risk who consumed more than 1.5 servings per day, which was about a 59% higher abdominal obesity risk compared with non-consumers. Moreover, individuals with a low GRS had a sharp increase in abdominal obesity risk related to higher consumption of fried food, which largely explained the significant interaction in the analysis using continuous variables (Table 3). A previous study indicated that the abdominal adipose tissue is the primary site for immediate storage of diet-derived fat.40 Among participants with a low genetic risk of obesity, higher intake of fried food might prefer affecting the body's fat distribution rather than the total weight, as the latter is genetically more difficult to change. Unfortunately, few GWAS studies have been conducted for WC so far; thus, studies on whether the association between fried food intake and the risk of abdominal obesity is modified by the variants of WC are warranted in the future. Overall, our present results of a significant interaction between diet and genetic predisposition to obesity risk emphasize the importance of sample size and the accuracy of obesity risk prediction by the GRS. Moreover, our results underlying the assessment of genetic risk could identify that individuals at increased disease risk and persons at a low GRS may be more susceptible to fried food intake, thus causing their inherited obesity risk.
There are several possible explanations for the positive associations of fried food intake with adiposity risk. Frying process increases fat content but dehydrates greatly,41 which produces fried foods with a high energy density. Frying also advances food palatability by improving its flavor and texture, which can lead to excess energy intake, thus increasing adiposity development.13 In addition, edible oil would be deteriorated by oxidation and hydrogenation reactions during frying, resulting in the decline of unsaturated fatty acids but the increase of trans fatty acids associated with a higher risk of obesity.42 Another explanation is that acrylamide is generated from foods rich in protein and carbohydrate, such as French fries and potato chips, during the frying process,43 which could play a vital role in the development of obesity, mainly driven by involving inflammation and oxidative stress.44,45 The significant positive relationships between fried potato consumption and adiposity risk in our study could be implicated by the association of acrylamide intake with obesity incidence. Previous epidemiological studies have supported this evidence that greater consumption of food containing a high acrylamide content was related to a higher risk of obesity and atherosclerotic lipid changes.46,47
The biological mechanisms underlying the observed interactions between fried food consumption and genetic predisposition to abdominal obesity risk remain unclear. Previous studies observed that fried food consumption was correlated with poor physical activity and excessive energy intake.17,41 Consistently, we also found that participants with greater fried food intake were more likely to have an unhealthier lifestyle, lower household income, poor sleep score, and higher total energy intake.17 Nevertheless, the documented interaction did not change after further adjustment for multiple lifestyle and dietary factors. Genetic variants such as FTO and MC4R associated with the regulation of appetite might personalize the effect of fried food consumption on adiposity.48,49 Previous evidence has also reported that FTO genetic variants could modify the function of total fat,50 saturated fat,51 and total energy intake on adiposity development.52 In this study, we found that fried food intake significantly interacts with individual's genetic risk on obesity incidence by calculating the cumulative effects of BMI-associated genetic variants including 940 SNPs. Notably, fried food intake affected individuals with a lower genetic risk more pronouncedly. Among individuals with high genetic burden of obesity, the influence of fried food intake might be weak, because the genetic factor may be the dominant factor, whereas individuals with a lower genetic risk may be mainly affected by dietary factors.53 However, the biological mechanism requires more research studies, especially experimental studies.
Our study had important strengths, including the use of a validated 24 h recall questionnaire for comprehensive assessment of dietary intake, objectively measured biomarkers of adiposity free of recall error from self-reports, a large sample size, and a long follow-up duration. We also had detailed information on multiple covariates that could potentially modify the relationships between fried food intake and obesity risk, which provided adequate statistical power to investigate the impact of fried food. Notably, we constructed novel polygenic scores of adiposity that capture 940 SNPs identified to be associated with BMI, which provided an accurate genetic risk prediction to fully examine the potential interactions in the gene–diet analyses.
Several limitations deserve attention. First, because our study was observational, the causal relationship between fried food intake and genetic risk and the development of obesity could not be inferred. Unmeasured or residual confounding factors could also not be completely ruled out, although we have comprehensively adjusted for potential confounding factors. Second, despite 24 h recall being acknowledged as the priority method for comprehensively recording dietary data, the information on the types of oil used for frying, frying time and temperature, frying method (deep, stir-frying, and griddling), and how often oil had been reused remains unclear. Although we further adjusted for the total energy intake, it was not possible to examine whether the interactions between fried food consumption and genetic predisposition to general obesity and abdominal obesity risk differed by these factors. Besides, inevitable measurement errors remained for 24 h dietary recall, such as recall bias and misreporting, though we had calculated an intake level of each food for all participants. Third, previous evidence indicated that obese individuals were more likely to underestimate the intake of unhealthy foods, such as snacks and French fries.54 Such underestimation of fried food consumption would dilute or attenuate the real relationships between fried food consumption and adiposity risk toward the null. Nevertheless, online questionnaires would have helped improve the accuracy of dietary intake, which is expected to minimize reporting bias due to societal expectations. Finally, due to the inclusion of European descent, our findings might not be immediately generalized to other ethnic groups.
| BMI | Body mass index |
| WC | Waist circumference |
| BF% | Percentage of body fat |
| GRS | Genetic risk score |
| HR | Hazard ratio |
| CI | Confidence interval |
| GWAS | Genome-wide association study |
| SNP | Single-nucleotide polymorphism |
| AMED | Alternate Mediterranean diet |
| MET | Metabolic equivalent of task |
Footnote |
| † Electronic supplementary information (ESI) available. See DOI: https://doi.org/10.1039/d3fo02803h |
| This journal is © The Royal Society of Chemistry 2024 |