Low Fat Diet or Low Carb Diet?

http://www.nytimes.com/2014/09/02/health/low-carb-vs-low-fat-diet.html

This is a great controversial article I found on the New York Times website! There is currently a lot of attention surrounding whether a low fat diet or a low carbohydrate diet is better for weight loss and overall health. As we all have seen with the multitude of diets that have come and gone in the media, there is a forever changing idea of "what we should eat". In class, specifically NTR 201, we learn what the body actually needs to function properly while maintaining homeostasis. This article presents the facts observed in a scientific study, comparing a group of individuals who followed a low fat diet and a group who followed a low carbohydrate diet. Upon first reading it, it seems the skies have opened and we now have the answer to all of our weight loss questions. But looking further, and using our education in nutrition, we can see the flaws in the content of this article. First off, fats and lipid digestion is a much slower and more complex process than that of carbohydrates, causing a person to feel satiated for longer after a high fat meal. This could be the cause of the loss of weight between the two groups, as one was eating less. Also, the body looks for glucose to burn as fuel first- it is the preferred source for brain and neuro function, and drives physical movement. When your diet consists of more carbs, there is never a need to tap into stored glucose as it is always readily available for use. When your diet consists mostly of fats and proteins, your body will search for this glucose in stored areas (such as muscles and liver) and when that is tapped, your body will go into ketosis; breaking down fats incompletely to obtain the energy needed for life processes. This causes fat to be burned up, hence why that group lost weight, however it leaves ketone bodies circulating in the blood stream (something you don't want!) The national guidelines for healthy consumption do promote unsaturated fats. They are not the heart disease causers- they are omega 3's, 6's, and many others that your body needs and wants- this article mentions very briefly that they were instructed to have unsaturated fats, no wonder their LDL's didn't skyrocket. Lastly, the loss in lean muscle mass is because they were not consuming enough protein to keep their muscles functioning how they were. Muscle is built by protein, more protein does in fact contribute to more muscle and lack of protein will in fact decrease lean muscle mass. These were just a few issues I noticed with this article! I would think if we looked at the actual study itself we might find more!

Lindsey Green

Obesity runs in families…but exactly how remains a mystery!

Of all inherited traits, obesity is one of the strongest.  However, despite enormous advances in genetics research over the past two decades, very little progress has been made in untangling exactly how genetic factors work to determine body weight.   The magnitude of genetic influence on the current obesity epidemic also remains to be determined.

A recent article in the Nature Outlook Supplement underscores the complexity of the issue and outlines where we currently are in our understanding.    

The author, Cassandra Willyard, explains: “Many scientists had first assumed that the heritability of obesity would be explained by common genetic variants.  But that hasn’t held true.”  The genome-wide association studies (GWAS), from which we’ve obtained most of our information about obesity genetics, have revealed many common variants, but all together these explain less than 5% of the variability that is attributed to genetics.   One scientist quoted in the article refers to this as the “dark matter of quantitative genetics”.  There is agreement among scientists that up to 70% of body weight variability is due to genetic factors even though no one can yet explain how this works.   Three possible answers are provided in the article: 

One possibility is that some genetic variants related to obesity have yet to be discovered.   Since GWAS can only identify variants common in greater than 5% of the population, less common variants may yet emerge and may demonstrate a more pronounced impact on obesity than the common variants.

Another interesting possibility is that our genes must interact with our environment to be expressed.  The GWAS study methods simply can’t account for this complexity yet.  One featured study showed that individuals with one common genetic variant were predisposed to eat greater quantities of food and weighed, on average, 6.6 pounds more than those without the variant.  Men in this variant group were also shown to have higher levels of the appetite-stimulating hormone ghrelin.  The best evidence we have so far though is from a large meta-analysis study which showed that people who carry a common “susceptibility gene” have a higher risk of obesity, but that this risk is much lower in people who are physically active.   In this case, a single environmental influence in essence protects individuals from their genetics.   What’s suggested is that our current obesigenic environment may exert much more influence on some individuals than others purely based on their individual biology.

Also intriguing is the evidence that gene expression is strongly influenced by the intrauterine environment.  The concept of “fetal programming”, as the author puts it “raises the possibility that a mother’s experiences during pregnancy –such as malnutrition – can influence the next generation.”   Put another way, lifestyle factors during pregnancy can influence an offspring’s  gene expression without altering the genetic code – and may also alter gene expression in the offspring’s offspring.   “When a pregnant woman experiences malnutrition or some other environmental stress, three are directly exposed – the mother, the child in her womb and also her grandchildren."  This presents one more way obesity can be “passed down” among generations.  A father’s exposure and lifestyle habits appear to have some influence as well, though the effect appears not to be as strong or persistent. 

 Overall, an interesting dynamic in the nature vs. nurture discussion is emerging.  We know that as obesity rates have risen in the past 30 years, our environment has changed dramatically, while our genetic code has not.  We also know that up to 70% of variation in body weight is attributed to genetics.  It seems gene-environment interactions – particularly in utero - may prove to be the missing link.  So, while our genetic code has not changed, our genetic expression has and these changes are now being passed down through successive generations.   

More to the Energy Balance Equation?

Thought of the day: Telling someone who's overweight to "just eat less and move more" is analogous to telling someone who's poor to "just make more money and spend less"!