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I have posted a a few articles which emphasized the detrimental consequences caused by obesity. Obesity is a major global health issues which increases year after year even with lots of interventions and awareness programs directed by some organizations. During the last three decades (30 years), the number of obese people, globally, had increased threefold from 857 millions documented in 1980 to approximately 2.1 billion documented in 2013. This increasing trend does not only affect high-income countries but low income countries as well. Nutritional transitions coupled with reduced in physical activities due to rapid urbanization has played a major role in contributing the increasing number of obese people. Even though it is proven by multiple studies conducted in the past that obesity can increase the chances of getting chronic diseases such as cardiovascular diseases and diabetes mellitus type II, little is known about the effect of obesity on cognitive function and brain structures.

In 1982, Masoro published a paper entitled "**Action of food restriction in delaying the aging process**" which explained the role of dietary restriction on longevity. The conclusion was dietary restriction will increase the average and maximum life span of an individual. Studies in 2009 involving animals, has shown that dietary restriction can attenuate brain atrophy as the consequences of aging processes in monkeys. This animals usually is being given about 60-70% from the ad libitum feeding allotment that is being given to the control animals (in another words, the test subject was being given 30% less calorie than the other group (control groups)).

# Ad libitum feeding  is to provide free access to food and water which allowing the animals to eat and drink whenever they felt the urges to.

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Another way of subjecting this animal to caloric restrictions is through intermittent fasting. In 2003, a study conducted by Anson RM et al, has found that chronic intermittent fasting in mice for 20 weeks caused an increase in hippocampal neuron actions towards excitotoxic stress. This action however, is not observed in the mice which consumed ad libitum caloric restriction foods which suggest intermittent fasting could provides neuroprotective effects to the brain. 

In 2013, Liaoliao Li has published a paper which shows that, intermittent fasting improved brain structures and function in mice which lead to an improved memory and learning. Multiple studies have shown that caloric restriction and intermittent fasting; both will increase the expression of brain derived neurotrophic factor (BDNF) which could lead to an increase of neuronal connections in the brain to improve learning and memory. The measurement of BDNF in the mice which underwent caloric restriction and intermittent fasting were found to be insignificant but the amount of oxidative stresses in the mice which underwent intermittent fasting were found to be much lower than the mice underwent caloric restriction. Since oxidative stress plays a major role in **brain aging**, **cell injury** and **learning and memory impairment**, the reduction of oxidative stresses in intermittent fasting can contribute to an improved brain functions and structures in mice.

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From the evolutionary perspective, severe food and caloric deprivation in animals can cause atrophy of certain organs except for brain. This suggest that even with the absence of food for fuels, the cognitive functions of the brain were still preserved. This is an important features so that the host (animals) can think clearly on how to find or hunt for food. The hungrier they are, the smarter they become. Some journals suggested that, mental activities of all mammals were increased during hunger and decreased when we feel satiated. 

# **References**
- Masoro EJ, Yu BP, Bertrand HA (1982) Action of food restriction in delaying the aging process. Proc Natl Acad Sci U S A 79: 4239–4241
- Witte AV, Fobker M, Gellner R, Knecht S, Floel A (2009) Caloric restriction improves memory in elderly humans. Proc Natl Acad Sci U S A 106: 1255–1260
- Colman RJ, Anderson RM, Johnson SC, Kastman EK, Kosmatka KJ, et al. (2009) Caloric restriction delays disease onset and mortality in rhesus monkeys. Science 325: 201–204 
- Anson RM, Guo Z, de Cabo R, Iyun T, Rios M, et al. (2003) Intermittent fasting dissociates beneficial effects of dietary restriction on glucose metabolism and neuronal resistance to injury from calorie intake. Proc Natl Acad Sci U S A 100: 6216–6220 
- Duan W, Guo Z, Jiang H, Ware M, Li XJ, et al. (2003) Dietary restriction normalizes glucose metabolism and BDNF levels, slows disease progression, and increases survival in huntingtin mutant mice. Proc Natl Acad Sci U S A 100: 2911–2916
- Li L., Wang Z., Zuo Z. Chronic intermittent fasting improves cognitive functions and brain structures in mice. PLoS One. 2013;8(6):e66069.