Diets that are high in added sugars and saturated fat have an impact on cognitive functioning, especially on memory. Cognitive task performance worsens with age. However, the frequency of consuming different types of foods (healthy versus unhealthy dietary patterns) moderates the effects of age on cognitive functioning. Different indices of dietary patterns (both positive and negative) seem to be strong predictors of cognitive performance in the older adult group.
1. Introduction
Age-related cognitive decline is associated with the deterioration of many cognitive dimensions, including memory, cognitive control, attention, and working memory
[1,2,3][1][2][3]. Diet is an important factor that may counteract age-related cognitive decline
[4]. Further, research has shown that the hippocampus, a brain structure associated with a wide range of cognitive functions, may be influenced directly by diet or by diseases related to diet and eating habits, such as obesity or diabetes
[5,6][5][6].
Diet is an integral part of preventing civilization diseases (e.g., obesity, diabetes, cardiovascular diseases) and medical treatment
[7[7][8],
8], and an important factor for mental health and cognitive performance
[9,10,11][9][10][11]. The Mediterranean diet (MD) is considered to be one of the best dietary models for healthy aging and has been shown to decrease risk factors for cardiovascular diseases and dementia, for example
[11]. The MD is a dietary pattern rich in antioxidants and, as such, has been suggested to have a protective effect on cognitive decline and dementia risk
[11,12][11][12]. Fish is one of the key components of the MD and fatty fish is a good source of omega-3 polyunsaturated fatty acids (PUFAs), which are neuroprotective. Indeed, a recent large observational study reported that adherence to the MD was associated with a decreased risk of cognitive impairment and higher fish consumption was also associated with slower cognitive decline within the context of the MD
[13]. Omega-3 PUFAs may also benefit memory performance by improving functional hippocampal connectivity
[14].
In contrast, diets high in saturated fat, sugar, and animal protein and low in fiber, known as the Western diet (WS diet), have negative effects on health
[4,15][4][15]. The WS diet lacks important polyphenols and anti-oxidant, may contain too little beneficial omega-3 PUFAs
[5[5][8],
8], and may cause mood and cognitive functioning decline
[16] through hippocampus-dependent memory and learning deterioration
[6,17,18][6][17][18]. It also leads to higher consumption of high-energy foods (especially high in saturated fat) and worsens hippocampus functioning, which may result in weight gain through behavioral changes
[19,20][19][20].
Moreover, hippocampal-dependent memory deteriorates throughout the lifespan
[21,22][21][22]. Attuquayefio et al. (2016) reported that being on a WS diet for only four days was sufficient to cause higher blood glucose levels, which resulted in worse memory task performance
[23]. Glucose in circulating blood can facilitate cognitive functioning, especially by enhancing memory performance
[24], but the quality and quantity of consumed products that are converted into glucose in the body are an important factor
[25]. Lastly, the WS diet may cause blood–brain–barrier disruption and hippocampal-dependent memory deterioration
[6,26][6][26].
Lipids are crucial for the development of the central nervous system
[27] and PUFA is an important factor for maintaining brain functioning, e.g., synaptic plasticity or regulation of neurotransmission
[28]. Horman et al. (2020) showed that the consumption of diets high in omega-6 PUFA, but with lower omega-3 PUFA, and conversely, changed the PUFA composition in brain structures, such as the hypothalamus, hippocampus, and prefrontal cortex
[29]. Another study showed that even a short-term high-fat diet may increase the levels of corticosterone in the hippocampus and impair memory consolidation in rats
[30]. The hippocampus is a structure responsible not only for memory and learning but also for controlling digestive functioning through hunger and satiety regulation
[17]. The WS diet impairs hippocampal functioning and leads to a deficit in memory performance
[31[31][32],
32], resulting in weakened inhibitory control that leads to greater consumption of high-fat foods, further impairment, and weight gain
[20,33][20][33].
The aim of the present research was to evaluate whether the type of food products and the frequency of their consumption are associated with cognitive functioning and whether they can moderate age-related changes in cognition. Age is an important factor in the deterioration process of a wide range of cognitive functions, and changes in the brain can alter cognitive functioning as early as just after the age of 35
[34]. We recruited participants in a wide age range to study the relation between diet and cognitive performance in various age groups.
Our main hypothesis was that high consumption of WS diet food products would result in a decrease in the performance on cognitive tasks, especially in the memory aspect. However, as cognitive functioning worsens with age we have also assumed that there are interaction effects of age and food patterns, with healthy foods diminishing the negative influence of age and unhealthy foods magnifying it.
2. Development and Findings
The aim of this study was to determine whether higher consumption of specific food products might affect cognitive functioning depending on age. Our results showed that the frequency of different food consumption might moderate the effects of age on cognitive functioning in both positive and negative directions. We found a negative effect of meat and animal fat consumption on memory, especially in people of older age. Interestingly, also in the older-aged group, higher consumption of white meat and fish was related to better performance in our memory task.
Aging is associated with an increase of inflammation, which has a negative impact on synaptic plasticity and neurogenesis
[42,43,44][35][36][37]. Saturated fat, which occurs in red meat or high-fat dairy products
[45][38], may increase inflammation in response to hormonal changes
[46][39]. Alternatively, omega-3 PUFA, which occurs in fish meat
[47][40], could prevent neuroinflammation changes in the hippocampus
[28].
In our study, age groups did not differ according to the means of pro-healthy and non-healthy diet indexes (
Table 1). The maximum values of pro-healthy and non-healthy diet indexes were 47 and 50 respectively, which means that our respondents’ dietary patterns were neither healthy nor unhealthy. This allowed us to focus on the frequency of consumption of specific products within the same diet. In addition, 172 participants declared an omnivore diet and only 9 participants were vegetarian, but as they consumed animal protein and animal fat from food products such as eggs or cheese, we decided to include them in further analyses. However, the differences in extracted consumption pattern indexes were related to a different aspect of cognitive functioning among the age groups.
Table 1. Participant characteristics, descriptive statistics, and test differences for: I. all participants, II. each age group.
Characteristics |
I. All (n = 181) Number/Mean (SD) |
II. Age Group ≤ 35 (n = 102) Number/Mean (SD) |
II. Age Group ≥ 36 (n = 79) Number/Mean (SD) |
II. Test Differences for Age Groups |
Sex |
♂ 92; ♀ 89 |
♂ 46; ♀ 56 |
♂ 46; ♀ 33 |
X2: 3.071 |
Age |
35.5 (9.2) |
28.7 (4.3) |
44.2 (5.8) |
t: −20.061 *** |
Employment |
83.50% |
82.4% |
84.8% |
X2: 0.194 |
Education |
|
|
|
X2: 0.858 |
secondary |
38.1% |
35.3% |
|
|
|
X |
2 |
: 0.002 |
omnivore |
95% |
95.1% |
94.9% |
|
vegan |
5% |
4.9% |
5.1% |
|