April 10, 2013
Adipose Tissue Resting Energy Expenditure Higher in Women than Men

Apologies for the period of dormancy.  I’m back and I’m bringing you new articles every Wednesday.  With that said, here we go.

Introduction:  Men and women store fat on different areas of the body.  Women store fat in larger amounts of subcutaneous adipose tissue (the fat under the skin) and men store more visceral fat (the fat around the organs).  In general, women have more body fat than men.  How much adipose tissue contributes to whole body metabolism is not well known; therefore, this was the aim of the study.

Methods:  This was a large cohort coming from hundreds of men and women.  The researchers looked at adipose tissue gene expression as well as expression of genes involved in mitochondrial function.

Results: 

  • For the two sexes, fat mass and fat free mass positively correlated with resting metabolic rate (when one went up, the other went up).  
  • Women have a higher metabolic rate per kilogram adipose tissue than men.
  • Women have a higher expression of genes related to mitochondrial function than men.
  • Women have a higher number of brown adipocytes in subcutaneous adipose tissue than men.

Discussion:  Just to give you an idea of the relative contributions of tissue to basal metabolic rate (BMR), the brain and internal organs account for 70-80% but only make up 5% of the body weight.  Skeletal muscle, which everyone in your gym says influences BMR the most, is 20 times lower than the internal organs.  Skeletal muscle accounts for about 15% of a person’s BMR.  Adipose tissue falls in at around 6% of BMR so we can say it is not that active of a tissue.  

From the lab to the gym: So what’s the main takeaway of this study?  The practical message is from bullet point 4 of the results and particularly a molecule found in those brown adipocytes known as UCP1.  UCP1 is a protein that allows the mitochondria to create heat in the brown adipocytes.  Women have a higher amount of UCP1 in their subcutaneous adipose tissue (the fat you want to lose under your skin).  Therefore, this study suggests that women have a higher capacity to burn calories by converting energy to heat.  Of course the internal organs and muscle are going to contribute the most to your BMR, but the higher metabolic rate of adipose tissue in women gives them an advantage to burn more calories in a resting state than men.

Nookaew et al J Clin Endocrinol Metab. 2013 Feb;98(2):E370-8.

March 5, 2012
Early Stage Subcutaneous Adipose Tissue Remodeling

How would you like to be in a study where they fatten you up for 2 months?  Well, this group recruited volunteers just for that and have provided a significant advancement in what is known about adipose tissue structural changes during the first several weeks of weight gain.

Introduction:  The purpose was to examine molecular changes in adipose tissue structure after 2 months of an overfeeding protocol. 

Methods:  Forty-four healthy males were recruited and told to increase their daily caloric consumption to excess of 760 kcal/day.  To accomplish this, they added 100 grams of cheese, 20 grams of butter, and 40 grams of almonds to their usual diet.  Fat biopsies were taken at 2 weeks and again at the end of the 2 months.

Results:  MRI revealed a significant increase in abdominal tissue volume both for subcutaneous and visceral.  No changes in mean adipocyte (fat cell) surface size or number.  There was a significant increase in the density of capillary vessels.  As you would expect, there was an increase in the number of genes related to fatty acid and lipid biosynthesis.  There was also an upregulation in genes involved in formation of the extracellular matrix and angiogenesis (the creation of blood vessels).

Discussion/Conclusion:  Although there was an increase in genes responsible for storing excess fat, there was not yet a significant increase in size or number of fat cells.  Interestingly, there was an upregulation in capillary density and genes involved in creating more blood vessels to supply the adipocytes.  This could also be a reason why the extracellular matrix was remodeled to create space during initial weight gain.

My input:  There were also some other important molecular pathways that were downregulated in this study but for sake of boring you I decided to leave those out.  I think the main important finding in this study is the disovery of genes involved in creating new blood vessels for the fat cells.  It makes sense if you think about it, that an increase in adipose tissue would demand a larger supply of blood.  Therefore, it is necessary to increase the amount of vessels perfusing the cells.  This group did well in not only showing this in gene arrays but also in histological staining from the fat biopsies.   Another article from a different group found similar results in that the adipose tissue of obese and insulin resistant subjects had larger vessels but fewer capillaries when compared to lean subjects.  I would not be surprised to see pharmaceutical studies in the near future aiming at trying to reduce the amount of blood vessels as a way to amerilorate adiposity.  After that, I would not be surprised if that is soon the next gimmick in supplement companies’ “fat burners”/thermogenic products.

Alligier et al  J Clin Endocrinol Metab. 2012 Feb;97(2):E183-92.

February 16, 2012
Where your body deposits fat matters in regards to insulin resistance and future cardiometabolic risk.  Here is a figure from a brand new study published by my doctoral adviser in Obesity.  Getting around the ugly statistical box plots, what it means to you is simply that subcutaneous thigh adipose tissue appears to show a protective effect when it comes to insulin resistance (Dr. Amati uses Rd in this case, which is rate of glucose disposal, as a marker of insulin sensitivity).  The higher you are on the scale, the more sensitive your periphery is to insulin.  The worst marker of insulin sensitivity, and what scientists can deem as the dangerous area to store fat, is the visceral abdominal adipose tissue.  These results are all regardless of age and gender.  
Here we see again the apple vs. the pear story in how one stores fat depots where in this case, the pear seems to win, or at least, be favored.

Where your body deposits fat matters in regards to insulin resistance and future cardiometabolic risk.  Here is a figure from a brand new study published by my doctoral adviser in Obesity.  Getting around the ugly statistical box plots, what it means to you is simply that subcutaneous thigh adipose tissue appears to show a protective effect when it comes to insulin resistance (Dr. Amati uses Rd in this case, which is rate of glucose disposal, as a marker of insulin sensitivity).  The higher you are on the scale, the more sensitive your periphery is to insulin.  The worst marker of insulin sensitivity, and what scientists can deem as the dangerous area to store fat, is the visceral abdominal adipose tissue.  These results are all regardless of age and gender. 

Here we see again the apple vs. the pear story in how one stores fat depots where in this case, the pear seems to win, or at least, be favored.

September 23, 2011
"Starvation mode"

You hear this term used a lot in the fitness realm, but I doubt any self-proclaimed guru or personal trainer can even begin to explain the scientific basis for it.  This post was sparked by a question that I received earlier and I thought I would take the time to display some of the most recent findings when it comes to to this theory.  How recent might you ask (which really means is Nick going to link us to more journal articles?).  My answer is as recent as of today (and no).  This time I’ll do all the writing for you, so for those of you who can’t stand doing any reading on your own, I urge you to please take the time to read the below paragraphs so you can learn for yourself what starvation mode is and how to get around it.

Today I attended an obesity conference with some big time names in the field of thermogenesis and body composition.  When I say big time, I mean big time.  Lewis Landsberg came up to my poster and asked me a question (this guy worked in the lab of a gentlemen who received a Nobel prize).  Anyways, I’ll be posting more from this conference within the next few days but now I shall highlight for you now some of the recent ideas when it comes to “starvation mode”.  Okay I promise you can read the one below now for the science.

Starvation mode is actually referred to in the scientific community as “Catch-up Fat Phenotype”.  Maybe this doesn’t sound as smooth as starvation mode but the main driving theory behind this is the classic hunter-gatherer lifestyle.  That is to say, our ancestors from thousands of years ago were primed to go through pro-longed periods of not having food; thus, retaining fat stores to provide energy.  The first basis of this came from a study published in 1950 known as the Minnesota Experiment by Keys et al which found that when individuals are suppressed of food for a period of 12 weeks, once refed, the body would “catch up” or at least try catch up to the weight they had before.  During the period of starvation, their non-specific thermogenesis would decrease and then increase back to normal upon refeeding.  This led scientists, specifically Abdul Dulloo, to investigate the role of adipose tissue in this Catch-up Fat Phenotype.  What he states is that thermogenesis is suppressed by adipose tissue because fat has a desire to save energy, hence the relationship with the hunter-gatherer lifestyle.  Adipose tissue does so by decreasing thermogenesis, which subsequently will reduce calories being utilized in the body and eventually, metabolism as you know it.  Now your next question might be, well what is the exact physiological mechanism for how “starvation mode” works?  During periods of starvation or low-calorie deficits for those dieting for weight loss purposes, skeletal muscle net utilization of glucose decreases which in turn decreases thermogenesis even more due to muscles high metabolic rate in the body.  In addition, the glucose that is not being used by the muscle is then sent to fat, which utilizes the glucose to increase adipogenesis (creation) of more fat, hence where the catch-up fat comes from.  Starvation processes lead to the eventual resistance of drivers of thermogenesis through this mechanism.

To conclude, you must refeed yourself to get out of starvation mode and continue your weight loss endeavors.  Adipose tissue is stubborn and has the ability to program itself to conserve energy from the fat depots that remain.  Give yourself calories to lose more weight? It sounds crazy, but based off of these findings it is the correct way to restore your metabolism back to normal so you can return to a level of burning the remaining fat that you have.  The period that you add back your calories will be long enough to restore your metabolism but not long enough to put fat on again.  Try a period of underfeeding for 6-12 weeks with a refeeding period of 1-2 weeks.  Play around with changing the weeks and see what works best for you.  There is a lot of individual differences when it comes to metabolism, even in twins.