Obesity is a major epidemic in modern society and an issue that is showing no signs of slowing down.
Society does have a growing focus on weight loss and dieting, but obesity continues to be a major problem.
In fact, many people find that they cannot lose weight or that they cannot keep off any weight that they have lost.
Excess weight is a significant health issue – and has been associated with many negative health outcomes.
Some of these negative outcomes are well known, including diabetes and metabolic syndrome, as well as issues with joints and mobility.
Yet, obesity can also have impacts on the brain.
One mechanism for this may be a connection between autophagy and the brain, much like the potential connection between autophagy and weight loss.
A recent study (Dong et al., 2015), argued that obesity’s impact on the brain may mean that the obesity acts as a risk factor in the development of neurological disease.
Specifically, the authors argued that a high calorie diet is a key risk factor.
They also argued that, by extension, a long-term low calorie diet has the potential to reduce the risk of neurological disease.
A key part of their argument was the process of autophagy.
Autophagy is a process that has been getting a lot of attention recently, especially in relation to weight loss.
The term roughly translates to ‘eating self’ or ‘self-eating’, It is a recycling process that occurs normally in the body.
Additionally, autophagy can also be trigged by some external conditions, including stress and starvation (1).
Many people argue that autophagy is an essential biological process, one that may contribute to overall health and even to weight loss.
The topic is an interesting one, because in modern society people often eat because food is appealing or simply because it is time to eat.
As a result, many people rarely feel hungry and certainly never let themselves stay hungry for any length of time.
In fact, the proposed benefits of autophagy are one of the reasons that intermittent fasting is promoted. Likewise, it is one reason that some people choose to skip breakfast.
There are certainly a number of people suggesting that autophagy and weight loss are connected.
After all, if our habits prevent autophagy from occurring as often as it should, what implications does this have for our health overall?
This study looked specifically at the impact of high versus low calorie diets on the brain.
The authors wanted to know what changes occurred in the brain and whether the different diet types could affect the brain.
The Study Itself
The first thing to note about this study is that it used animals as subjects rather than humans.
Specifically, the study involved the use of 30 male mice.
These mice were split into three groups and each group was given a different diet.
One of those groups continued on a regular diet (the control), one on a low calorie diet and the last on a high calorie diet.
The mice then followed this diet for 10 months and were weighed every month.
Because of the life cycle of mice versus humans, the study design essentially meant that the mice were following those diets in the long-term.
In contrast, you would probably have to follow humans for 5 years or more to look at long-term impacts in that way.
The authors also tested other outcomes, including behavior and aspects of the brain.
In particular, the authors used trials to test the behavior of the mice.
Following the behavioral testing at the beginning of the study, the authors also anesthetized half of the mice from each group and tested their brains biochemically.
The authors noted that across the study, the high calorie group of mice gained weight (compared to the control) while the low calorie group lost weight (compared to the control).
In both cases, those changes were statistically significant.
The high calorie group also reached a level of weight associated with obesity.
The authors found that the high calorie group of mice did have impaired cognitive function compared to the other two groups.
Additionally, the low calorie group performed the best cognitively.
The authors suggested that these results could mean that calorie restriction can help to delay some of the impacts of aging and also promote the process of autophagy.
Throughout their data, the authors consistently found that the high calorie and the low calorie diets had opposite effects on the brain.
Limitations of the Study
The very nature of this study does significantly limit the conclusions that we can draw from it.
In particular, the research involved the use of animal models (mice in this case) and a consideration of the way that aspects of the animals changed in relation to different levels of calorie intake.
Animal models are sometimes used to prove that a line of inquiry is worth following.
In this way, studies using animals can be used to justify more expensive and involved research on humans.
In some cases, animal studies might also be used because the study design would be too expensive to conduct in humans or it would be unethical.
For example, it is possible to subject animals to a range of experimental conditions, then look at what changes occurred in the brain.
Such an approach might require killing the animal, so conducting the same study on humans would not be possible.
So, there are some very important reasons that a study might use animal models.
Additionally, animal models are used in research because they do have some predictive value.
This means that in many cases, humans will respond in a similar way to the animals.
In this case, the authors showed that long-term high calorie intake was associated with suppressing the process of autophagy and contributing to the development of neurological disease.
In contrast, there was a connection between autophagy and weight loss, with autophagy seeming to occur more in the low calorie diet, where mice also lost more weight.
That outcome suggests that a similar pattern may also be present in humans.
However, because the study was conducted in mice, we have no way of knowing whether similar effects would occur in humans.
Overall, this means that the study suggests that such a relationship might be present and strongly supports the need for research in humans.
A second issue is that a low calorie diet for mice is likely to be significantly different than for humans.
So, the study does not give any indication about the specific levels of calorie intake that would have effects on humans.
And, as Precision Nutrition points out, nutrition science is confusing at the best of times. The research is inherently difficult and there simply aren't any easy answers many of the key questions.
Implications of the Study
The use of animals in this study might be a limitation, but the study does also show some important information.
In particular, it shows that calorie restriction may be beneficial for the brain while high calorie intake may have the opposite effect.
Generally speaking, most people don’t consider cognition when thinking about their diet or the implications of their diet for health.
It’s also important to note that this is not the first study to consider this topic.
For example, one study argued that the connection between calorie restriction and aging (including the cognitive component of aging) has been known since 1917, although the area is certainly controversial (2).
Likewise, research has suggested that inhibiting autophagy can contribute to aging (3).
So overall, this study is a strong indication that low calorie diets may be more beneficial than people often assume.
Realistically, low calorie diets are a powerful way of losing weight anyway, so this study may offer one more reason to give a low calorie diet a try. But, if you're following this idea, make sure you're eating healthily and getting enough nutrients.
After all, as Everyday Health points out, too few calories can be bad for health and don't necessarily help weight loss either.
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What do you think? Can a low calorie diet improve mental functioning?