1. Introduction
Cardiovascular disease (CVD) is the leading cause of death in the United States, and the risk is often exacerbated by a poor diet [
1]. Saturated fatty acids (SFA) and trans fatty acids (TFA) have been widely understood to have a negative effect on serum cholesterol profiles, thereby increasing the risk of CVD [
2,
3,
4,
5]. Numerous randomized controlled trials [
6,
7,
8] and prospective observational studies [
9,
10,
11,
12] have provided strong and consistent evidence that a decrease in dietary SFA reduces the risk of CVD events and all-cause mortality.
Worldwide guidelines have promoted the replacement of SFA with polyunsaturated fatty acids (PUFA), while suggesting that TFA intake should be entirely avoided. The current American Heart Association and American College of Cardiology (AHA/ACC) guidelines suggest a decrease in SFA intake to 5–6% of an individual’s total daily energy intake (%E) for those with elevated low-density lipoprotein cholesterol (LDL-C) concentration [
13]. The 2015–2020 US Department of Agriculture Dietary Guidelines for Americans also recommends consuming <10%E from SFA for the general population, as well as the replacement of SFA with unsaturated fats [
14]. Similarly, the National Lipid Association Expert Panel strongly recommends a healthy diet low in SFA (<7%E) [
15]. However, despite these recommendations, SFA intake remains high in the United States [
16].
Metabolic syndrome (MetS) is associated with an increased risk of developing CVD and Type 2 Diabetes Mellitus (T2DM) [
17,
18], and nearly 35% of US adults and 50% of those aged ≥60 years suffer from MetS in 2011–2012 [
19]. Epidemiological studies have demonstrated that higher SFA and TFA intake are modifiable dietary risk factors for MetS [
20,
21,
22,
23]. However, current SFA and TFA intake and meal-consumption patterns among MetS patients remain elusive. The purposes of AHA dietary recommendations are to promote a healthy diet and lifestyle, and since 1961 the AHA has suggested a reduction in dietary SFA and TFA in order to reduce the risk of CVD [
13]. However, to our knowledge, there has been no research so far aimed at evaluating the effectiveness of dietary counselling, based on the AHA dietary guidelines, in decreasing SFA and TFA intake.
In this study, we investigated the effect of AHA-based dietary counselling on SFA and TFA intake among individuals with MetS. At the same time, we explored changes in SFA and TFA in different meal types, meal location, and day of the week. We hypothesized that the AHA dietary counselling would decrease SFA and TFA intake.
3. Results
The present investigation included 119 obese subjects with MetS (BMI: 34.9 kg/m
2, 95% CI 34.4 to 35.5). The average age was 52.5 years old (95% CI 50.7 to 54.3 years), and 85 of the 119 participants (71%) were women. Mean attendance to AHA dietary counselling was 7.9 sessions (standard deviation (SD) = 3.9) out of a total of 14 sessions. Baseline SFA and TFA intake by demographic characteristics are presented in
Table 2. SFA intake was significantly higher in males (
p-value = 0.001 for g/day) and among Caucasians (
p-value = 0.038 and
p-value = 0.020 for g/day and % E). TFA intake was significantly higher in those with lower household income (
p-value = 0.028 for g/day). During the one-year study, a total of four adverse events were reported. It was determined that the causes of these adverse events were not treatment-related (hysterectomy, pneumonia, lung cancer, and kidney stones).
Figure 1 illustrates the improvement in compliance, between the baseline and the one-year study visit, with the AHA recommendations for total fat, SFA, and TFA intake among study participants. After one-year dietary counselling, percentage of participants who were compliant with the AHA dietary guidelines fat intake recommendations as %E increased from 25.2% to 40.2% for total fat intake (
p-value = 0.02); from 2.5% to 20.7% (
p-value < 0.01) for SFA intake; and from 45.4% to 62% (
p-value = 0.02) for TFA intake.
The comparison of selected daily fat intake (both g and %E) between baseline and one-year follow-up visit are presented in
Table 3. Average intake of total fat, SFA and TFA decreased from 74.8 g/day, 26.4 g/day and 2.7 g/day at baseline to 54.4 g/day, 16.7 g/day and 1.6 g/day at one-year (all
p-values < 0.01); and the corresponding %E decreased from 33.1%, 11.6% and 1.2% to 31.1%, 9.7% and 0.9% (all
p-values < 0.01). Intake as g/day of total monounsaturated fatty acid (MUFA), oleic acid, total PUFA, linoleic acid (LA), and alpha linolenic acid (ALA) decreased significantly over the one-year period (all
p-values < 0.05); however, their intakes as %E did not decrease. Only the intake as %E of arachidonic acid (AA) decreased significantly (
p-value = 0.021). Meanwhile, total energy intake decreased significantly after the one-year AHA counselling (
p-value < 0.01).
Table 4 and
Table 5 demonstrate the SFA and TFA intake by meal type, location, and day of week. Overall, for SFA, subjects consumed less when they ate at home with significant one-year differences in intake observed at breakfast (from 4.54 g to 2.48 g,
p-value < 0.05), lunch (from 7.53 g to 5.13 g,
p-value < 0.05), dinner (from 10.05 g to 6.51 g,
p-value < 0.05), and snack (from 4.03 g to 2.09 g,
p-value < 0.05). Subjects also consumed significantly less at lunch at one year when they ate in a restaurant or fast food outlet (from 10.24 g to 6.53 g,
p-value < 0.05). At the same time, SFA intake from weekday breakfast, dinner, and snacks and weekend lunch, dinner, and snacks decreased significantly from baseline to one-year (all
p-values < 0.05). However, significant decrease of SFA intake as %E was only observed with snacks consumed at home (from 10.37% to 7.95%,
p-value < 0.05) and away from home (from 11.13% to 7.06%,
p-value < 0.05) after the one-year counselling.
Compared to baseline, TFA intake after the one-year counselling decreased when subjects ate at home, with significant differences observed for dinner (from 0.90 g to 0.60 g, p-value < 0.05) and snacks (from 0.42 g to 0.17 g, p-value < 0.05). For meals consumed in a restaurant/fast food chain, TFA intake during lunch decreased significantly at one year (from 1.81 g to 0.95 g, p-value < 0.05). At the same time, TFA intake from lunch in weekend days decreased significantly from baseline to one-year (from 1.12 g to 0. 52 g, p-value < 0.05). TFA intake as %E from different meal locations and days of week between baseline and one-year visit were similar.
4. Discussion
The present study indicates that the proportion of participants complying with the AHA dietary guidelines for intake of total fat, SFA, and TFA significantly increased after the one-year AHA dietary intervention, by 60%, 800% and 36%, respectively. Correspondingly, significant decreases were observed for daily intake of total fat, SFA, and TFA (both in g/day and as %E). Additionally, SFA intake for all meal types at home decreased significantly. Nevertheless, the SFA intake from a large proportion (79.3%) of participants still exceeded recommended limits.
Dietary SFA intake is not only associated with risk of CVD, but also negatively affects bone mineral density [
29] and cancer [
30,
31,
32,
33,
34]. Foods containing a high proportion of saturated fat include animal products such as cream, cheese, butter, other whole milk dairy products and fatty meats. Certain vegetable products also have high saturated fat content, such as coconut oil and palm kernel oil. Many prepared foods are high in saturated fat content as well, such as pizza, dairy desserts, and sausage. While not all SFA are metabolized the same, detrimental effects of diets rich in total SFA have been widely recognized, and national nutritional guidelines have emphasized the need to replace SFA intakes with unsaturated fats. The implementation strategy currently recommended to achieve the reduction of dietary SFA is to shift from food choices high in saturated fat to those high in polyunsaturated and monounsaturated fats [
13,
14]. However, this is not only about a better choice of oils, but about shifting away from some foods to others that may be quite different in taste, texture, and overall dietary pattern. To achieve meaningful SFA reductions, the country requires strong public health policies providing information on SFA content alerting customers to improve their food choices; in addition to consumer education and agreements with food producers to limit the use of SFA.
Dietary TFA can be naturally derived from ruminant-based meat and dairy products, or artificially through partially hydrogenated oils (PHOs) in the food industry and manufacturing processes [
35]. By the late 1990s in the United States, most TFA in the diet (79%) came from PHOs [
36]. In our study, the biggest contributors of TFA were meat, poultry, and fish recipes (12.47% at baseline vs. 18.75% at one year), followed by breads, rolls, biscuits, and other related products (10.75% at baseline vs. 10.70% at one year) (data not shown in table). In the United States, nutritional labelling of TFA content became mandatory in 2006 [
37]. In 2007, New York City (NYC) became the first in the United States to pass a regulatory restriction on PHO use, targeting restaurants. In June 2015, the US Food and Drug Administration (FDA) announced that PHO use in foods would be phased out of the US market by June 2018, as they were not considered safe for consumption [
38], although companies have now been granted an extension to January 2020 [
39]. Our study showed that the percentage of participants who complied with AHA dietary recommendations, the daily intake of TFA (both g/day and %E), and TFA intake for dinner and snacks at home, have all improved after the one-year AHA dietary counselling. Education to encourage consumers to further change their dietary patterns and increase healthy cooking at home are needed, and the FDA recommendations to restrict the use of industrially produced TFA in restaurants should be strictly enforced.
PUFAs have usually been shown to be associated with beneficial health effects on CVD. Omega-3 PUFAs have been demonstrated to decrease the production of inflammatory mediators, having a positive effect in obesity, diabetes, and MetS. Moreover, they significantly decrease the appearance of CVD risk factors [
40,
41,
42]. As for MUFAs, cumulative evidence indicates that dietary MUFAs prevent or ameliorate MetS and CVD risk by favorably modulating blood lipids, blood pressure and insulin sensitivity [
43,
44,
45]. Moreover, the majority of epidemiological data favor the cardioprotective activity of dietary MUFAs [
43,
46]. In the present study, we found that intake in grams of MUFA, oleic acid, total PUFA, LA, ALA significantly decreased after the one-year counselling; however, their intake as %E did not decrease. Only the intake as %E of AA decreased significantly. Therefore, the significant decrease as g/day may be a result of reduced total energy intake. The AHA dietary counselling in our study was based on the 2006 AHA guidelines, which did not include replacing SFA with PUFA, as recommended in the present AHA guideline [
47]. Therefore, we did not observe significant change of unsaturated FAs, except AA, after the one-year counselling.
One of the strengths of our study is the use of three 24-h dietary recalls, which offers information on intake from individual foods, being more precise than Food Frequency Questionnaires, which include mostly food groups [
48,
49]. Additionally, to our knowledge, this is the first study that reports detailed FA intake and evaluates the effect of the AHA dietary counselling among MetS patients. Long-term management of MetS by consumption of a healthy dietary pattern plays an important role in improving health and quality-of-life outcomes. At the same time, we are looking in detail at changes in SFA and TFA in different meal types, meal location, and day of the week, which is an additional strength of our study.
Several limitations should also be considered in light of these results. First, there was no control group without AHA dietary counselling in this investigation, which limited the interpretation of the results. Second, our study was based on the 2006 AHA guidelines, which did not include replacing SFA with PUFA as recommended in the present AHA guidelines. Third, not all SFA generate the same effects. For example, stearic acid has a neutral effect on total cholesterol (TC), LDL-C, and HDL-C, whereas lauric, myristic, and palmitic acids increase TC, LDL-C, and HDL-C, with myristic acid having the most potent hypercholesterolemic effect [
50,
51,
52]; the type of saturated fat found in dairy products may be protective for chronic disease [
53,
54,
55,
56]. However, we only calculated the data for total SFA intake, and analyzed the change of total SFA. We decided to focus on the effect of AHA diet on total SFA intake in this manuscript as this is the current dietary recommendation, thus, further research is needed. Lastly, our findings were obtained from obese adults with MetS (BMI between 30 and 40 kg/m
2) and the sample size is limited, and therefore it is inadequate for generalization to other populations in the United States.
In conclusion, the one-year AHA dietary counselling increased the proportion of participants complying with the AHA guidelines for dietary intake of total fat, TFA and most prominently SFA, which increased eightfold. However, there is still room for considerable improvement, particularly in levels of SFA intake. Actions that further encourage low-SFA and low-TFA food preparation at home, and strong public health policies that decrease SFA and TFA in restaurants and prepared foods are needed.