A study involving 110 lean and healthy students (aged 20-23) found that those randomly assigned to a high energy western-style diet for a week performed worse on a memory test compared to those who ate their normal healthy diet. Moreover, those on the unhealthy diet then showed a greater tendency to eat more sugary foods.
Data from the large and very long-running Framingham Heart Study has revealed that people who drink sugary drinks frequently are more likely to have poorer memory, smaller overall brain volume, and a significantly smaller hippocampus. Moreover, a second study found that those who drank diet soda daily were almost three times as likely to develop stroke and dementia over a 10-year period, compared to those who didn’t – suggesting that substituting artificial sweeteners for the sugar doesn’t make matters better.
A trial in which 163 overweight adults with elevated blood pressure were given one of four complete diets that contained all their food for five weeks has found that a low glycemic diet did not improve insulin sensitivity, lipid levels or blood pressure. But it's important to note than all diets were based on a healthful DASH-type diet, varying only in their glycemic index and carbohydrate proportions.
So, the trial found that a healthy diet with low–glycemic index carbohydrate-containing foods didn't improve insulin sensitivity, HDL cholesterol levels, LDL cholesterol levels, or systolic blood pressure any more than the healthy diet with high–glycemic index foods It did reduce plasma triglyceride levels slightly more.
In fact, the low–glycemic index with high-carbohydrate diet was worse than the high–glycemic index, high-carbohydrate diet — decreasing insulin sensitivity and increasing LDL cholesterol and LDL apolipoprotein B levels. This finding was unexpected and inconsistent with other research. However, a meta-analysis of 28 trials found that lowering glycemic index did not affect HDL cholesterol or triglyceride levels and lowered LDL cholesterol level only if fiber content was also increased.
In line with the researchers' previous findings, the DASH diet had slightly better effects when its carbohydrate content was reduced. When the same calories were instead supplied by unsaturated fat and protein, triglycerides and VLDL levels were substantially lowered and diastolic blood pressure slightly lowered.
As in previous trials, all the DASH-type diets lowered blood pressure and LDL cholesterol levels.
Previous research has shown inconsistent results on whether low glycemic index helped people lose weight.
http://www.eurekalert.org/pub_releases/2014-12/bawh-lgd121614.php
Sacks FM, Carey VJ, Anderson CM, et al. Effects of High vs Low Glycemic Index of Dietary Carbohydrate on Cardiovascular Disease Risk Factors and Insulin Sensitivity: The OmniCarb Randomized Clinical Trial. JAMA. 2014;312(23):2531-2541. doi:10.1001/jama.2014.16658.
Goff LM, Cowland DE, Hooper L, Frost GS. Low glycaemic index diets and blood lipids: a systematic review and meta-analysis of randomised controlled trials. Nutr Metab Cardiovasc Dis. 2013;23(1):1-10.
Following research showing that decreasing brain function in the area of the hippocampus called the dentate gyrus is a main contributor of normal age-related cognitive decline, an imaging study has been investigating the cause of this decreasing function by looking at measures that typically change during aging, like rising blood sugar, body mass index, cholesterol and insulin levels. The study of 240 community-based nondemented elders (average age 80 years), of whom 60 had type 2 diabetes, found that decreasing activity in the dentate gyrus only correlated with levels of blood glucose. The same association was also found in aging rhesus monkeys and in mice. The finding suggests that maintaining blood sugar levels, even in the absence of diabetes, could help maintain aspects of cognitive health. It also suggests that one reason why physical exercise benefits memory may be its effect on lowering glucose levels.
Mayeux, R., Vannucci, S. J., Small, S. A., Wu, W., Brickman, A. M., Luchsinger, J., … Barnes, C. A. (2008). The brain in the age of old: The hippocampal formation is targeted differentially by diseases of late life. Annals of Neurology, 64(6), 698-706. Retrieved from http://dx.doi.org/10.1002/ana.21557
http://www.eurekalert.org/pub_releases/2008-12/cumc-rac121508.php
A doctoral study has found that those given low glycemic index breakfasts could concentrate better and had a better working memory. Moreover, healthy individuals with low glucose tolerance (higher than average rises in blood sugar following a meal) generally performed less well. The study also found that eating the right whole-grains for breakfast didn’t simply regulate blood-sugar levels all morning, but all day — some ten hours. Experiments also showed that the blood sugar increase following breakfast can be moderated in a similar way by eating the right grain products the night before. Great variations in levels of blood sugar are being associated more and more with the risk of old-age diabetes, obesity, and cardiovascular diseases.
Nilsson, A. 2007. Effects of Indigestible Carbohydrates and GI of Cereal Products on Glucose Metabolism, Satiety and Cognitive Function in Healthy Subjects; Emphasising mechanisms for glycaemic regulation at the acute, second and third meal. Division of Applied Nutrition and Food Chemistry, Lund University, P.O Box 124, 221 00 Lund.
http://www.eurekalert.org/pub_releases/2007-09/src-rbb090507.php
A new study takes an important step in explaining cognitive impairment in diabetics, and suggests a possible cause for some age-related memory impairment. The study assessed non-diabetic middle-aged and elderly people. Those with impaired glucose tolerance (a pre-diabetic condition) had a smaller hippocampus and scored worse on tests for recent memory. These results were independent of age or overall cognitive performance. The brain uses glucose almost exclusively as a fuel source. The ability to get glucose from the blood is reduced in diabetes. The study raises the possibility that exercise and weight loss, which help control blood sugar levels, may be able to reverse some of the memory loss that accompanies aging.
Convit, A., Wolf, O. T., Tarshish, C., & de Leon, M. J. (2003). Reduced glucose tolerance is associated with poor memory performance and hippocampal atrophy among normal elderly. Proceedings of the National Academy of Sciences of the United States of America, 100(4), 2019-2022. Retrieved from http://www.pnas.org/content/100/4/2019.abstract
http://www.eurekalert.org/pub_releases/2003-02/nyum-hsb013003.php
On four occasions, a small group of older people ( 61–79 years) were given, after the night's fast, either a drink containing protein (whey), carbohydrate (glucose), fat (safflower oil), or a nonenergy placebo. Cognitive tests were given 15 and 60 minutes later. Only the carbohydrate drink increased blood glucose levels, but all 3 of the energy drinks improved memory for paragraphs. Other memory improvements were specific to the type of drink. For example, fat was the only one that enhanced attention. In general, improvement was greater 60 minutes after drinking than 15 minutes after.
Kaplan, R. J., Greenwood, C. E., Winocur, G., & Wolever, T. M. (2001). Dietary protein, carbohydrate, and fat enhance memory performance in the healthy elderly. Am J Clin Nutr, 74(5), 687-693. Retrieved from http://www.ajcn.org/cgi/content/abstract/74/5/687
http://www.eurekalert.org/pub_releases/2001-10/ajoc-ecr101901.php
A study of 41 healthy seniors aged 60 to 84 found that memory function was improved after a breakfast of wholegrain unsweetened cereal, milk, and juice (compared to no breakfast). This improvement was greatest for those with memory problems and those with early signs of adult-onset diabetes. The study was carried out by researchers at the Baycrest Centre for Geriatric Care at the University of Toronto.
Findings were presented to the Society for Neurosciences 2000 annual meeting in New Orleans.
http://www.baycrest.org/news_archive_2001_breakfast_memory.htm
A review and meta-analysis of all international studies that compared the effects of higher versus lower added sugar consumption on blood pressure and lipids (blood fats or cholesterol) has uncovered evidence that sugar has a direct effect on risk factors for heart disease, and is likely to impact on blood pressure, independent of weight gain.
http://www.eurekalert.org/pub_releases/2014-05/uoo-sii051414.php
In a large Mayo Clinic study, self-reported diet was found to be significantly associated with the risk of seniors developing mild cognitive impairment or dementia over a four-year period.