Is being skinny genetic
Is being skinny really down to genetics? Nature study suggests so
Scientists may have identified the first genetic link to being underweight. A paper published in the journal Nature this week found that people with extra copies of a region of chromosome 16, locus 16p11.2, have a significantly increased risk of being underweight.
Researchers from Imperial College London and the University of Lausanne in Switzerland studied a large group of patients with developmental and intellectual disabilities. They found that men who had a duplication of locus 16p11.2 were 23 times and women five times more likely to be underweight than those who did not.
Underweight patients had a body mass index (BMI) of less than 18.5, whereas healthy people have BMIs between 18.5 and 25.This follows previous observations that people who are missing this same genetic locus are at an increased risk of being morbidly obese.
In general, people have two copies of each gene, one from each parent. However, it is not uncommon for a copy to be deleted or duplicated. Often this has no visible effect but having too few or too many copies of certain genes can sometimes lead to disease.
Professor Philippe Froguel from Imperial's School of Public Health, who led the research, said it is the 'first example of a deletion and a duplication of one part of the genome having opposite effects'.
Locus 16p11.2 contains 28 genes, any of which could be responsible for the effects on body weight. 'We now plan to sequence these genes and find out what they do, so we can get an idea of which ones are involved in regulating appetite', Professor Froguel said.
The Nature paper also showed a strong link between this locus and head size. A quarter of patients with a duplication of 16p11.2 had microcephaly, where the head is abnormally small, whereas those with a deletion of the locus had larger heads.
This is consistent with the known link between this group of genes and cognitive disorders, which could be related to impaired brain development. Head size was also correlated with BMI.
'This is the first genetic cause of extreme thinness that has been identified. One reason this is important is that it shows that failure to thrive in childhood can be genetically driven. If a child is not eating, it's not necessarily the parents' fault', Professor Froguel said.
What are the risks of being underweight?
If a person is underweight, their body may not be getting the nutrients it needs to build healthy bones, skin, and hair. Related symptoms or signs can include osteoporosis, anemia, feeling tired, and more.
While some people may have a genetic background or a medical illness that prevents them from putting on weight, there are interventions doctors can recommend to help a person gain weight.
In this article, we look at ways to tell if you are underweight, causes, treatments, and when to see a doctor.
The Centers for Disease Control and Prevention (CDC) recommend people use a body mass index (BMI) to calculate if they are underweight, at a healthy weight, or overweight.
Using the BMI is considered a good measure of a persons weight because it compares their weight to their height. For example, a 170-pound person may not be overweight if they are very tall but could be overweight if they are very short.
A person can calculate their BMI by visiting the CDCs
- Underweight: less than 18.5
- Normal/healthy weight: 18.5 to 24.9
- Overweight: 25.0 to 29.9
- Obese: 30 or higher
These calculations may be slightly inaccurate for a person who is an elite or endurance athlete whose body has a significant amount of muscle. This is because muscle weighs more than fat.
Being underweight can cause health problems, just as being overweight can.
Not all people who are underweight experience adverse side effects or symptoms from being underweight. However, some people, experience the following symptoms related to being underweight:
- Osteoporosis. According to a
2016 study , being underweight increases a womans risk of osteoporosis, which is where the bones are brittle and more prone to breaking. - Skin, hair, or teeth problems. If a person does not get enough nutrients in their daily diet, they may display physical symptoms, such as thinning skin, hair loss, dry skin, or poor dental health.
- Getting sick frequently. If a person does not get enough energy from their diet to maintain a healthy body weight, they may also not be getting enough nutrients to fight off infections. As a result, a person may get sick more frequently, and common illnesses, such as a cold, can last longer than they usually would.
- Feeling tired all the time. Calories are a measurement of the energy a particular food can give a person. Not getting enough calories to maintain a healthy weight can make a person feel fatigued.
- Anemia. A person who is underweight is more likely to have low blood counts, known as anemia, which causes dizziness, headaches, and fatigue.
- Irregular periods. Women who are underweight may not have regular periods, they may find menstruation stops, or an adolescents first period may be delayed or absent. Irregular or absent menstruation can cause infertility.
- Premature births. According to a study published in
An International Journal of Obstetrics & Gynaecology , a woman who is pregnant and underweight is at a higher risk for pre-term labor, which means having a baby before 37 weeks. - Slow or impaired growth. Young people need nutrients to grow and develop healthy bones. Being underweight and not getting enough calories could mean a person may not develop as expected. Doctors call this a failure to thrive.
According to a study published in the journal
There are a variety of reasons why a person may be underweight. Sometimes, multiple underlying causes may be related. Causes of being underweight include:
- Family history. Some people have a naturally low BMI due to physical characteristics that run in their family.
- A high metabolism. If a person has a high metabolism, they may not gain much weight even when eating high-energy foods.
- Frequent physical activity. Athletes or people who engage in high levels of physical activity, such as runners, may burn significant amounts of calories that result in low body weight.
- Physical illness or chronic disease. Some disease types can cause regular nausea, vomiting, and diarrhea, making it difficult to gain weight. Other conditions may decrease a persons appetite, so they do not feel like eating. Examples include cancer, diabetes, thyroid disorders, and digestive conditions, such as Crohns disease or ulcerative colitis.
- Mental illness. Poor mental health can affect a persons ability to eat, including depression, anxiety, obsessive-compulsive disorder (OCD), and eating disorders, such as anorexia and bulimia. Each of these conditions can affect a persons body image and appetite.
A doctor can help a person identify the cause of their low BMI and recommend a treatment plan that allows them to gain weight healthfully.
If a person is underweight, there are various healthful weight-gain methods that they can try.
A person can gain weight by following a healthful diet that incorporates nutritious calorie-dense foods. A doctor may recommend a person tries a specific diet for weight gain or refer them to a dietitian, who can help a person develop a diet plan that works for them.
Some key components of a diet for weight gain may include:
- Adding snacks. High-protein and whole-grain carbohydrate snacks can help a person gain weight. Examples include peanut butter crackers, protein bars, trail mix, pita chips and hummus, or a handful of almonds.
- Eating several small meals a day. Sometimes a person may be underweight because they cannot tolerate eating large meals. Instead, a person can eat several small meals throughout the day.
- Incorporating additional foods. A person can add calorie-dense food sources to their existing diet, such as putting slivered almonds on top of cereal or yogurt, sunflower or chia seeds on a salad or soup, or nut butter on whole-grain toast.
- Avoiding empty calories. Eating high-calorie foods may cause a person to gain weight, but they also have excess fats that could affect a persons heart and blood vessels. A person should avoid foods that are high in sugar and salt.
Doctors may also prescribe anti-nausea medications or appetite stimulants to help a person who is underweight gain weight whenever possible. Doctors will usually only prescribe these treatments when at-home treatments have not worked.
A person should see their doctor if they have tried to gain weight but have not been able to. Anyone who is experiencing any effects of ill health due to being unable to gain weight, such as missed periods or infertility, should also see a doctor.
If a person struggles with mental illness or an eating disorder, it is essential they seek professional help. Unfortunately, a person may not always recognize their behavior is a problem.
Some of the symptoms associated with eating disorders include:
- secretive behavior
- sudden, unexplained weight loss
- refusal to attend family or social events
- appearing fatigued
- refusing to eat in front of others
If a person has these symptoms, their friends or family members should encourage them to seek professional help from a doctor or therapist.
A person who is underweight may be at an increased risk of developing complications, including bone, teeth, and fertility problems.
A person should aim to maintain a healthy BMI. Working with a medical professional can help a person achieve and sustain a healthy weight.
What factors affect the size of a penis?
Many males may have concerns about the size or appearance of their penis from time to time. People may wonder if penis size is genetic. We address whether this, and any other factors, play a role in determining penis size.
While it is true that people can consider penis size to be a genetic trait, many other factors impact penis size. These factors include hormones, nutrition, and diet.
In this article, we explore factors that affect penis size, average penis length, and the risks of penis enlargement methods.
Genes are the building blocks that determine a living organisms appearance and behavior. Humans inherit two copies of each gene, one from each parent. Multiple genes make up chromosomes.
Humans have 23 pairs of chromosomes. Of these, there are 22 autosomes and one set of sex chromosomes.
A persons sex chromosomes determine their biological sex and secondary sexual characteristics.
Males inherit one Y chromosome from their male parent and one X chromosome from their female parent. Females inherit two X chromosomes, one from each parent.
The Y chromosome carries genes that oversee the development of male genitalia and fertility.
The Y chromosome determines the development of the penis and testes but not necessarily penis size or girth. These characteristics may be dependent on the X chromosome.
The X chromosone contains
This difference may explain why penis size varies among siblings with the same biological parents.
Genetic mutations may also affect penis size and appearance as well as other physical characteristics.
While quite rare, genetic conditions sometimes influence penis size include Kallmann syndrome and Klinefelter syndrome.
Thus, penis size depends on a combination of a persons parental genes, their own unique genes, and other external factors.
The following factors also affect penis size:
Hormones
Just as estrogen and progesterone affect female sexual characteristics, such as breasts, hips, and fat storage, male sex hormones, or androgens, contribute to testicular and penile growth.
During puberty, the pituitary gland produces more luteinizing hormone (LH) and follicle-stimulating hormone (FSH).
LH promotes testosterone production in the Leydig cells of the testicles, and FSH promotes sperm production.
Variations in testosterone levels during pregnancy may cause penile abnormalities. For example, the mother may not produce enough human chorionic gonadotrophin (hCG) hormone. The hCG hormone stimulates testosterone development in the fetus.
Rare conditions, such as 5 alpha reductase deficiency and congenital adrenal hyperplasia, also affect testosterone levels and may affect genital appearance.
Even if testosterone levels are normal, some medical conditions may stop a persons body from responding to testosterone correctly. This response is called androgen insensitivity.
When any of these hormonal issues arise, the penis of a male fetus may not develop in the usual way.
Environment
Environmental pollutants, such as pesticides, plasticizers, and other chemicals, may have a negative effect on penis size. These chemicals may act as
Epigenetics is a growing area of science investigating how the environment may affect gene expression.
Studies in
A 2019 study also suggests that epigenetic-associated dietary influences may slow genital progression in adolescent boys.
Nutrition
Malnutrition in the womb and throughout life may impact hormones and affect growth and development.
Furthermore, malnutrition in adolescence, as is seen in anorexia or bulimia, can
While individuals undergoing delayed puberty typically catch up eventually, symptoms of delayed puberty include a smaller penis and testicles.
Other factors
Genetics are the strongest predictors of penis size. However, factors, such as body fat and the presence or absence of pubic hair, can make the penis appear larger or smaller without affecting its true size.
When exposed to cold temperatures, the blood vessels in the penis constrict. This physiological reaction causes the penis to shrink temporarily.
According to a
- 9.16 centimeters (cm) or 3.6 inches (in) when flaccid
- 13.24 cm or 5.2 in when stretched in a flaccid state
- 13.12 cm or 5.17 in when erect
The average penis circumference is:
- 9.31 cm or 3.6 in when flaccid
- 11.66 cm or 4.6 in when erect
Another 2014 article reported average erect penile dimensions based on the self-measurements obtained from 1,661 men.
The average erect penis length was 14.5 cm or 5.7 in, and the average erect penis circumference was 12.23 cm or 4.8 in.
However, as this study relied on the mens own measurements, the results may be less reliable. The researchers deemed the results were fairly consistent with prior research.
Click here to learn more about average penis size.
The penis enlargement or male enhancement industry claims that enlargement procedures, vacuum devices, pills, and creams increase penis size.
However, there is limited research for many of these methods, and they may come with serious risks.
The majority of people seeking penis enlargement have average-sized penises, meaning that they are of adequate size for sexual activity and urination.
The Urology Care Foundation only recommends penis enhancement surgery for people with a rare condition called micropenis where a penis is two or more standard deviations below the average size.
The American Urological Association states that there is not enough high-quality evidence to support the safety or efficacy of penile augmentation surgery.
Potential risks of trying to increase penis size include:
- swelling, infection, or scarring after surgery
- damage due to overusing a vacuum pump or stretching devices
- contact dermatitis that topical products may trigger
- allergic reactions to ingredients in pills
- erectile dysfunction
Click here to learn more about penis enlargement methods.
Genetics plays a substantial role in determining penis size. However, other factors, such as hormones, the environment, and nutrition, can affect penis size.
Other factors, including body type, physical fitness, and underlying medical conditions may affect how the penis appears and a persons perception. However, it is important to note that most people fall into the normal range of penis sizes.
A person should speak with a doctor if they are concerned about the size or appearance of their penis.
