Sense of smell and obesity

A new study has found a link between sense of smell and obesity.  A recent review of this study concludes that people with obesity have a reduced ability to detect and discriminate smell compared with those who are not obese.
Woman using sense of smell while cooking
A recent review highlights a possible link between obesity and olfaction.

Obesity is a medical condition characterized by an excessive amount of body fat.

It is a global issue that affects millions of people worldwide, and it is a risk factor for diabetes and heart disease.

Doctors or nutritionists can identify obesity using the body mass index (BMI). The BMI is a diagnostic tool that assesses if a person is an appropriate weight for their age, sex, and height.

According to the World Health Organization (WHO), global obesity has nearly tripled since 1975.

In 2016, almost 2 billion adults were overweight, of which 650 million were obese. In the same year, 41 million children under 5 years old were overweight or obese.

In 2013, the American Medical Association (AMA) recognized obesity as a disease. The decision changed the way the medical community related to this complex issue. The ruling challenged the widespread idea that obesity is the direct consequence of eating too much and not doing enough physical activity. The AMA argued that “some people do not have complete control of their weight.”

Surprising link between weight and smell

The relationship between the sense of smell and body weight was a relatively unknown area of scientific study and knowledge, up until now. Researchers from the University of Otago in New Zealand recently discovered a surprising link between obesity and the ability to smell. The team published its findings in Obesity Reviews.

The study involved researchers from Otago’s Departments of Food Science, Anatomy, and Mathematics/Statistics. The scientists gathered scientific papers regarding the link between body weight and sense of smell. They also collected information of nearly 1,500 individuals from “empirical and clinical worldwide studies.”

“After compiling our evidence, we found there is, in fact, a strong link between a person’s body weight and their smell ability — the better a person can smell, the more likely the person is to be slim, or vice versa,” says Dr. Mei Peng, lead author of the study, from the University of Otago’s Department of Food Science.

Dr. Peng added that smell plays a critical role when it comes to eating behavior because it affects the way we identify and choose between different flavors. A poor sense of smell may result in people making unhealthful food choices, which can increase their risk of obesity.

For example, they might choose, or be more attracted to, saltier and tastier foods such as bacon and maple syrup instead of blander foods, such as low-fat cereal with less sugar.”

Dr. Mei Peng

Weight loss surgery could improve the sense of smell

The researchers found that people who were closer to obesity had a reduced ability to smell and identify odors. Based on these findings, the researchers hypothesized that obesity alters a person’s metabolism, which affects communication pathways between the gut and brain.

To re-establish the pathway between the gut and brain, researchers considered the effects of two surgical obesity treatments. They looked at stomach removal and gastric bypass (a surgical procedure which involves dividing the stomach into two pouches and rearranging the small intestine to connect to both).

The findings showed that stomach removal could improve the sense of smell, while other obesity surgeries do not have the same effect.

“Cutting the stomach could change nerves in the stomach that affect the gut-brain pathway, so smell changes could be the key to the difference between the two surgeries — essentially, the smaller size of the stomach might not be the factor that leads to weight loss, it is more likely due to the gut-brain pathway being reset,” Dr. Peng concludes.

Dr. Peng hopes that these findings will increase awareness around the critical relationship between eating habits and senses. This groundbreaking study could deepen our knowledge of the role that “reward-factor smell has in various body-shape groups.”

Nuts and your health

Two new studies suggest that a small daily serving of nuts may benefit overall metabolic health and keep off the weight we tend to gain as we enter adulthood.
serving of nuts
A daily serving may prevent weight gain and improve metabolic health in the long run, two new studies suggest.

From providing cardiovascular benefits to potentially improving fertility, and even boosting memory and intelligence, the health benefits of nuts are numerous — and no wonder.  They are packed with unsaturated fatty acids, fiber, protein, and other beneficial chemicals, which may all contribute to good health.

However, can these dried seeds aid weight loss? Are certain types better able to support good metabolism?

Two new studies delved deeper into these questions. The authors will present the findings at Scientific Sessions 2018, a conference to be held by the American Heart Association (AHA) in Chicago, IL.

The first study — led by Xiaoran Liu, Ph.D., a research associate in the nutrition department of the Harvard T.H. Chan School of Public Health in Boston, MA — looked at the long-term effects of nuts and peanuts on body weight.

The second study examined the effects of Brazil nuts on satiety, blood sugar, and insulin response.

It was supervised by Mee Young Hong, Ph.D., a registered dietician and a professor in the School of Exercise & Nutritional Sciences at San Diego State University in California.

Nuts prevent weight gain in adulthood

The first study explored consumption in:

  • 25,394 healthy men who had taken part in the Health Professionals Follow-up Study
  • 53,541 women who had participated in the Nurses’ Health Study
  • 47,255 women who had taken part in the Nurses’ Health Study II

The three groups had filled in food frequency questionnaires once every 4 years.

The researchers discovered that replacing foods that had less nutritional value with a 1-ounce serving of nuts and peanuts lowered the risk of weight gain and obesity over the 4-year follow-up intervals.

More specifically, replacing a serving of red meat, processed meat, french fries, desserts, or potato chips with a serving of nuts correlated with significantly less weight gain in the long run.

The study’s first author comments on the findings, saying, “People often see nuts as food items high in fat and calories, so they hesitate to consider them as healthy snacks, but they are in fact associated with less weight gain and wellness.”

“Once people reach adulthood, they start to gradually gain about 1 pound a year of weight, which seems small. But if you consider gaining one pound over 20 years, it accumulates to a lot of weight gain,” Liu notes.

Adding 1 ounce of nuts to your diet in place of less healthy foods — such as red or processed meat, french fries or sugary snacks — may help prevent that slow, gradual weight gain after you enter adulthood and reduce the risk of obesity-related cardiovascular diseases.”

Xiaoran Liu, Ph.D.

Brazil nuts benefit insulin, glucose responses

In the second study, researchers examined the effects of consuming the Brazil variety in 22 healthy adult participants, 20 of whom were women.

The participants added either 36 grams of pretzels or 20 grams of Brazil nuts to their normal diet in two trials. At least 48 hours passed between trials.

The Brazil nuts and pretzels contained about the same number of calories and the same amount of sodium. Both triggered a sense of fullness, but the Brazil type contributed to an increased feeling of satiety.

Forty minutes after the participants had consumed their snacks, the researchers found that the pretzels had caused significant increases in blood sugar and insulin levels, whereas the Brazil nuts had not.

The study’s senior author explains, “While both Brazil nuts and pretzels increased a sense of fullness after they were eaten, eating Brazil nuts stabilized postprandial (after eating) blood glucose and insulin levels, which may be beneficial in preventing diabetes and weight gain.”

Although the study was observational, the researchers speculate that selenium may explain the benefits of Brazil nuts. Prior studies had linked the mineral with better insulin and blood sugar responses, and Brazil nuts are rich in selenium.

However, the researchers caution that because only 9 percent of participants were men, the study’s findings may not apply to all.

Our study allows researchers and clinicians to consider the possible beneficial role of Brazil nuts to help people feel full and maintain a healthy level of glucose, reducing the risk of obesity and diabetes.”

Mee Young Hong, Ph.D.