The effect of a pescatarian diet on the cognitive performance of older adults
with type-2 diabetes mellitus: A longitudinal intervention study
A Research Proposal
A longitudinal, single-arm nutrition intervention study with a pretest-posttest design would
be carried out to investigate whether or not adherence to a pesco-vegetarian diet supports
the maintenance of healthy cognition in older adults with type-2 diabetes, who are at a higher
risk of developing mild cognitive impairment (MCI) and dementias. 65 cognitively healthy,
community-dwelling adults with type-2 diabetes over the age of 60, who meet the initial
inclusion criteria, would be recruited from medical practices located in the X council area of
Scotland. The cognitive performance of the participants would be measured at baseline and
after two years of intervention using the Isaacs Set Test (IST) and Mini-Mental State
Examination (MMSE). Conformity to the intervention diet would be assessed by the
participants’ diet adherence scores, which would be determined via food diary analysis.
Background
With an estimated 47 million people currently affected worldwide, degenerative dementia
disorders incur substantial social and financial burdens (Dominguez & Barbagallo 2016). In
light of the rapid growth of aging populations and the lack of effective pharmaceutical
treatments to cure dementias, dementia risk reduction has been recognized by the World
Health Organization as an explicit priority (WHO 2017). Therefore, research on risk factors
such as nutrition, which are potentially modifiable and thus suitable for intervention, is of
enormous relevance.
Alzheimer’s disease (AD) followed by vascular dementia (VaD) are the most prevalent
forms of dementia, with AD accounting for 60-70% of the documented cases (Al-Assaf et al.
2015). While the early-onset familial type of AD is autosomal-dominant, this directly inherited
form is extremely rare (Borchelt et al. 1996). Most forms of the disease are sporadic;
characterized by complex interactions between genetic and environmental factors (Davey
2014). A principal marker for risk of sporadic AD (sAD) is age; with approximately 1-2% of
people aged 65 years being affected compared to as high as 30% of those aged 85 years
(Davey 2014, p. 504). Beside age, the presence of the e4 allele of the apolipoprotein E (APOE)
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, gene has been identified as an additional, unmodifiable risk factor for developing sAD (Farrer
et al. 1997).
Over the years, however, some potentially modifiable risk factors for AD have also been
proposed including smoking, physical and cognitive inactivity, depression, midlife obesity,
hypertension and diabetes (Barnes & Yaffe, 2011). In their meta-analysis of 28 prospective
observational studies, Gudala, Bansal, Schifano and Bhansali (2013) reported that individuals
with diabetes had a 56% and 127% increased risk of AD and VaD respectively, compared to
non-diabetic people. A meta-analysis of 19 longitudinal studies conducted by Cheng, Huang,
Deng and Wang (2012) yielded similar results, leading the authors to conclude that patients
with diabetes should be provided with MCI and dementia prevention strategies.
A growing body of empirical evidence now suggest that nutrition might play a role in the
prevention of age-related cognitive decline (Dominguez & Barbagallo 2016; Luschinger &
Mayeux, 2004). The pescatarian diet, which primarily refers to a lacto-ovo-vegetarian diet
supplemented with seafood, has been associated with a wide range of health benefits
(Thalheimer 2015). Firstly, adherence to such a dietary pattern has been linked to reduced
risks of developing numerous diseases including cardiovascular disease, obesity as well as
type-2 diabetes, which are all potential modifiable risk factors for degenerative dementia
disorders (Barnes & Yaffe 2011).
Tilman and Clark (2014) found that compared to conventional omnivorous diets, following
a pescatarian diet decreased a person’s relative risk of type-2 diabetes by 25%, cancer by 13%,
and of coronary heart disease by 21%. Furthermore, in a hospital-based survey study of 754
participants, Zaman, Zaman and Arifullah (2010) reported that the prevalence of type-2
diabetes mellitus was higher in non-vegetarians (8.2%) than in pesco-vegetarians (4.9%).
After adjusting for numerous confounding variables including sex, age, BMI, and physical
activity, the researchers concluded that increased adherence to some form of vegetarian,
including pescatarian, diet may protect against risk of type-2 diabetes. Although this study
suffers from low population validity due to its relatively small sample size, results from a large-
scale, cross-sectional study including 60903 participants by Tonstad, Butler, Yan and Fraser
(2009) also suggested that conformity to a pescatarian diet seems to afford intermediate
protection against both obesity and type-2 diabetes.
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