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Contents
- Does Race Affect Your Ability To Lose Weight?
- Differences In Obesity Occurrences Between African Americans & Other Ethnic Groups
- Does Race Affect Your Ability To Lose Weight? Understanding Metabolism
- Differences in Metabolism Among Races
- Possible Reasons For Differences In Metabolism Among
Those Of African Descent
- Practical Implications Of Racial Differences In Metabolism
Does Race Affect Your Ability To Lose Weight?
We know that a number of environmental and genetic factors influence our ability to lose gain weight, however the idea that race- or better yet, ancestral origin, may a role is relatively new. For example, it was believed (and is still taught today) that if two individuals of the same body mass and composition ingested the same amount of calories and did the same amount of physical activity, then the total energy used would be the same. A fact that would hold true regardless of whether the subjects were White, African American, Asian or Hispanic. It’s a premise that serves as the foundation for all the clinical diet and exercise recommendations made over the past several decades and you would think that these ideas were set in stone. However a body of research continues to show that differences in ancestry lead to very measurable and significant variations in metabolic rates. Variations that add even more complexity to the already complex issues of obesity, weight loss and weight gain, as studies consistently find that individuals of African descent appear to burn as much as 15% LESS calories at rest than an individual of European ancestry of equal body mass.[1,2,3,4] In this article we will take a look at the phenomenon of metabolic differences among individuals of different ancestral backgrounds and explore how relevant those differences may be. It’s a fascinating study and I encourage you to share it with anyone who you think might benefit from reading it.
Differences In Obesity Occurrences Between African Americans & Other Ethnic Groups
African Americans have a higher rate of obesity compared to all other ethnic groups in the US.
The finding that there are measurable differences in metabolism based on ancestral heritage does call into question the relevance of low calorie diets as a weight loss protocol in certain populations. Socioeconomic, cultural and dietary practices aside it also raises the issue as to why African Americans have higher risk of obesity, diabetes and the chronic metabolic related diseases that accompany obesity.[5, 6, 7] Of all the ethnic groups in the United States African American adults have the highest rates of obesity with an obesity occurrence of 45%. Contrast that number with the rate for Hispanic American adults which is 36% and Caucasian American adults at 30%. Adult African American women have even higher rates relative to other ethnic groups (49%) and in cases of extreme obesity where BMI is measured at over 40, African Americans have the highest percentage of adults in that range with 13.5% compared to 5.7% in Hispanic Americans and only 5.5% of Caucasian Americans.[15] These numbers remain higher even among African Americans children and adolescents who exhibit between 3-11% higher rates of obesity when compared to Caucasian Americans of the same ages.[15] It would be naïve to think that innate metabolic differences alone would account for such discrepancies in rates of obesity between African Americans and other ethnic groups, however it is a factor that does need to be explored.
Does Race Affect Your Ability To Lose Weight? Understanding Metabolism
There are two types of metabolism- voluntary and involuntary.
To grasp the implications of differences in metabolism we should start with a discussion of how our metabolism actually works. There are two ways that our bodies burn calories and that is through voluntary energy expenditure or involuntary energy expenditure. Voluntary energy expenditure refers to the energy we expend doing everyday activities such as walking, working, exercising and such. Voluntary energy expenditure is, (for the most part), selectively modifiable, as you can control how much energy you expend on a daily basis by doing more or less activity over the course of the day. The way our body uses energy is through involuntary energy expenditure, which refers to the energy our body and organs use in order for us to stay alive. Brain function, respiration, digestion, elimination, smooth muscle activity such as the beating of your heart and other organ functions are all completely out of our individual control and require a tremendous amount of energy. So much so that involuntary energy expenditure can make up as much as 60-80% of total energy expended on a daily basis. [4] An amount large enough to play a significant role with regards to calculating energy requirements for losing or gaining weight and as we have said, for many years it was thought that this aspect of metabolism (also called Resting Energy Expenditure or Resting Metabolic Rate) was a constant for everyone of equal body mass.
The standard (and somewhat flawed) method for calculating how much you should eat to lose weight is based on estimating your voluntary energy expenditure along with your resting metabolic rate and creating a diet with a calorie intake slightly lower than your energy needs. The theory is that if you frequently ingest less calories than you expend you will lose weight and that if you take regularly in more calories than your body can use, you will gain weight. Sounds simple enough, but it isn’t ever that simple as timing of meals and other factors can undermine energy balance and cause weight gain or retard weight loss even when calories are regularly lower than what your body needs. (See my article- ). One problem with the energy bane model is that energy expenditure is estimated using standardized charts and formulas that assume the same resting energy expenditure for individuals of equal body mass- which would lead to inaccurate calculations for many individuals of African descent as it would propose a diet that would contain more calories than would required to lose weight.
Differences in Metabolism Among Races
Studies have found that those of African ancestry have much slower resting metabolic rates when compared to other ethnic groups.
So how significant are the differences among individuals of different ancestral backgrounds? A peer reviewed study of over five thousand men and women found that individuals of African descent expended an average of 164 few kcal/day than those of European origin due to lower resting energy expenditure.[1] This discrepancy increased to as much as 308 kcal/day after adjusting for age, gender, education and income. [1] (Though not explored in depth in the study, Mexican Americans were surprisingly found to expend on average 211 kcal/day than individuals of European descent.) Another large scale study of 3075 people found remarkably similar differences between European Americans and African Americans as African Americans were observed to have a sleeping metabolic rate that was 85-100 kcal/day lower than that of European Americans of the same body mass.[4] The study found an almost identical 160 kcal/day difference between a population of individuals genetically confirmed through testing as being of African ancestry and a population confirmed to be of completely European origin.[4] Both studies found these differences to hold true even when taking into consideration differences in lean muscle mass and thyroid dysfunction.
Possible Reasons For Differences In Metabolism Among Those Of African Descent
Differences in organ size and energy metabolism may explain the reason why those of African descent have lower resting metabolic rates.
Researchers cannot conclusively pinpoint the reasons for these variations in metabolic rates but there are some theories put forward to account for the differences. One theory is that the smaller fractional mass of certain high metabolic rate organs in individuals of African descent explains the lower resting metabolic rate when compared to European Americans. [8, 9] Organs, brain matter especially, require a significant amount of energy for every day function and an MRI comparison of brain, liver, kidney, spleen and other organs between those of European ancestry and those of African descent found smaller organ sizes among those of African ancestry. When adjustments are made for lower metabolic requirements due to the relative organs size differences it seems to account for the differences in resting metabolic rates.[8,9,10]
Another theory places the differences as a result of selective changes brought on by environmental pressures when early humans migrated to higher latitudes.[11,12] The process of oxidative phosphorylation in the mitochondria generates ATP which is required for muscular contraction and is the main energy source for the majority of cellular functions. This mitochondrial process also reoxidizes the energy rich co-enzymes NADH and FADH2 which allow for continued generation of ATP and serves to regulates body temperature through heat production by the coupling state of the mitochondria.[13] A lower resting metabolic rate therefore would allow for maximizing the conversion of energy to ATP instead of heat- creating a rather energy efficient body able to do more physical activity, which makes perfect sense as a human living in tropical Africa where the environmental temperature is close to our own body temperature would not need to generate much in the way of excess heat. Energy that would be better used for physical and metabolic activity. Adaptive mitochondrial changes (mutations) brought on by the changes of environment and temperatures as humans migrated further away from the equatorial climate from which we originated developed a higher resting metabolic rate through higher rates of mitochondrial uncoupling.[12] Which allowed for greater body heat production in colder climates and also seems to have given those of European descent a method to compensate for high energy intakes in times of caloric abundance. A benefit that could help explain why African Americans have higher rates of obesity than those of European ancestry in our era of superabundant food supplies.[4] Is it a matter of smaller organ mass or mitochondrial adaptations or a combination of both? We don’t know exactly but what we do know is that it does change the landscape in terms of caloric intakes.
Practical Implications Of Racial Differences In Metabolism
The recommendation that African Americans should eat less than the average American & exercise more to lose weight is both flawed and impractical.
With this data in mind the studies conclude that African Americans would need to eat less calories than the average American or be more physically active than the average American in order to reduce their body weight below that of the average American.[1] Recommendations for lower calorie intakes are problematic however, as a significant body of studies confirm that low calorie diets are not effective long term for the general public.[20,21,22] As such a call for more stringent dietary practices for African Americans is somewhat impractical if the general population has a difficult enough time adhering to the conventional daily calorie recommendations to begin with. Furthermore, lowering calorie intake can also have the unwanted effect of lowering metabolic rate as the body goes into starvation mode in order to conserve as much energy as possible- a protective response left over from hundreds of thousands of years of surviving famines and inadequate food supplies. Lowering calorie recommendations could thus compound the problem and make weight loss even less likely. (See my article- ) Calls for increasing exercise and physical activity levels are always welcome among those in the fitness field who believe more time exercising is the universal answer to any weight or health related problem, but the reality of modern life makes the current recommendations of 2 ½ hours of exercise plus 2 bouts of strength training difficult for most.[17] Real world studies affirm that the number one reason for lack of adherence to an exercise program is lack of time[18] and in an era where most Americans are unable to meet even the minimum exercise guidelines, it’s overly idealistic to recommend an increase for African Americans.
Practical Solutions For Dealing With Lower Resting Metabolic Rates
Both recommendations are not viable solutions and if resting metabolic rate accounts for 70-80% of total daily energy expenditure the focus should be on increasing it. Apart from our organs, fat free muscle mass is the most metabolically active tissue in our body and increasing skeletal muscle mass through resistance type training leads to an increase in resting metabolism.[23,24] Skeletal muscle is also crucial for maintaining proper blood glucose levels and energy balance,[25] and increasing muscle mass through the use of high intensity protocols not only calls for shorter training times but also have the benefit of decreasing body fat as well through excess post exercise oxygen consumption. [26,27]
How Relevant Is Lower Metabolic Rates Among Those Of African Descent?
West Africans & West Indians of African descent have far lower rates of obesity than African Americans.
The problem with this body of data is that it is difficult to translate lower resting metabolic rates an actual cause of higher obesity rates in African Americans. We are hardwired to believe in causality- the idea that a single and easily understood factor is responsible for a particular phenomenon but as far as obesity is concerned, there is no single cause. Instead obesity is like a web of connecting environmental, genetic, dietary and activity related factors that manifest it and we must look at the evidence questioning the relevance of a lower metabolic rate to obesity as well. All of the studies found that correlation between lower resting metabolic rates and African ancestry, however the greater percentage of European ancestry, the higher the resting metabolic rate. This difference has been positively linked to single gene polymorphisms whose proportions vary by race [4] and each percentage increase in in the proportion of ‘European’ polymorphisms in those who identified as African Americans corresponded with an approximate 1.5 kcal/day increase in resting metabolic rate.[4]
We identify ourselves using cultural and physical attributes as a method of inclusion in any particular race or ethnic group, however, without genetic testing there is no concrete way to know what proportion of gene polymorphisms we carry from which group. This is especially true for African Americans who are the progeny of ancestors subjected to forced migration to the Western Hemisphere from Western Africa and enslavement for several hundred years- which often makes accurate estimation of bloodlines difficult if not impossible without genetic testing. Thus it’s hard for anyone identifying as African American to know how relevant resting metabolic rate differences would be for them as an individual without DNA analysis.
Furthermore, the prevalence of obesity and associated metabolic diseases is far lower among populations in West Africa and West Africans who have recently migrated to the United States [14,16,28] thus invalidating the possibility that a lower resting metabolic rate alone could be responsible for higher rates of obesity among those of African descent. Rates of obesity are on the rise in the Caribbean which also has a large population of West African descent as a result of the slave trade but are still not as high as among their African American counterparts.[14] This confirms that patterns and types of physical activity along with diet and physical fitness levels are far more relevant- as are differences in social and economic living conditions.[6]
In two decades of working with hundreds of individuals from every region on the planet, I have never encountered any differences in weight loss progress that could be attributed to ethnic origin. One explanation could be that a system based on increasing muscle mass and activity levels while keeping calories within moderate but never low ranges, might invalidate any differences in resting metabolism as it would increase resting metabolism regardless. What we do come away with from this data set is that blanket diet and exercise recommendations for the general public are impractical at best and misleading at worst given differences identified among populations and that any program of diet and exercise should be designed with the individual in mind.
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Kevin Richardson is an award winning health and fitness writer, natural bodybuilding champion and the creator of Naturally Intense High Intensity Training. His training company in New York City is the 2 time winner of the Best of Manhattan Awards for 2013 & 2012. Learn more about his diet and training services
References
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17. 2008 Physical Activity Guidelines for Americans
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Does Race Affect Your Ability To Lose Weight? [re: Mod vege]
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