Why skinny fat is bad for you

A friend recently asked: “I’m South Asian and people say I’m ‘skinny fat.’ What is that—and how can I prevent it?”

That question echoes something I’ve noticed for years: I see many lean Asian patients with type 2 diabetes. In medical school we’re taught that obesity drives diabetes—yet many of my Asian patients with severe diabetes are not obese.

I was stunned by this graph on the prevalence of diabetes among Asian American adults (reference):

Prevalence of T2D among individuals 45 to 84 years of age in Asian subgroups vs other ethnic groups. NH, non-Hispanic; NHPI, Native Hawaiian/Pacific Islander; and T2D, type 2 diabetes. Data derived from the 2020 US census

As you can see, every Asian subgroup living in the United States has higher rates of diabetes than non-Hispanic whites. Even more incredible: nearly 1 in 3 South Asians, Filipinos, and Native Hawaiian/Pacific Islanders in the United States between 45-84 years old is diabetic.

Unfortunately, it’s not just diabetes that is of higher prevalence in South Asians. A study conducted in my home state at Kaiser Permanente Northern California reviewing data from 2006 to 2016 showed a 2-fold higher rate of coronary artery disease in South Asians compared with Caucasians (reference).

What is going on here?

Could visceral fat explain some of this?

It turns out there is a medical term for skinny fat: normal weight “obesity”. This is when a person has a normal body mass index (BMI) but high visceral fat. Visceral fat is hidden deep inside our abdomen, surrounding our liver, pancreas and other organs. Unlike subcutaneous fat, visceral fat is metabolically active and releases free fatty acids and proinflammatory cytokines.

It is well established that visceral fat is a key driver of insulin resistance, type 2 diabetes, hypertension and cardiovascular disease. Studies that have measured subcutaneous and visceral fat using CT scans have shown that although the size of both fat deposits is associated with disease, individuals with excess visceral fat had more severe metabolic abnormalities (reference). Men with normal BMI’s but in the upper tertile of body fat percentage (>23% fat) were 4 times more likely to have metabolic syndrome and had a higher prevalence of type 2 diabetes, hypertension, and cardiovascular disease than those in the lowest tertile (reference). The news is worse for women: those in the highest tertile of body fat (>33% fat) were 7 times more likely to have metabolic syndrome. Skinny fat women (normal weight obesity) were almost twice as likely to die at follow-up as women in the lowest tertile of body fat.

We know that visceral fat increases with age, menopause, smoking, and sedentary lifestyle. What about ethnicity?

Do South Asians have more visceral fat?

Yes.

Scott et al evaluated 822 healthy Aboriginal, Chinese, European, and South Asian participants aged between 30 and 65 years old who were living in Canada (Multicultural Community Health Assessment Trial). They used CT and DEXA scans to assess total body fat and visceral fat. At the same body-mass index (BMI), South Asians had more total body fat and visceral fat than the Europeans. At the same amount of total body fat, both Chinese and South Asians had more visceral fat than the Europeans. The authors conclude, “The Chinese and South Asian participants possibly deposit more visceral fat per kilogram of total body fat than do the Europeans.”

Shah et al published compared the body composition of South Asian Americans to other ethnic groups (reference). They analyzed the results from the Mediators of Atherosclerosis of South Asians Living in America (MASALA, N=906) and the Multi-Ethnic Study of Atherosclerosis (MESA, N=6800, including whites, African Americans, Latinos, and Chinese Americans). They found that South Asians had greater visceral fat, greater intermuscular fat, and less lean mass than the other ethnic groups.

How to measure visceral fat

So how how can you determine if you have excess visceral fat? Weighing yourself or calculating your BMI is not good enough. Waist circumference (WC) is a much better measure. I wish doctors routinely measured not only blood pressure and weight, but also WC . For the general population, a WC > 40 inches for a man or > 35 inches for a woman is highly correlated with increased visceral fat. Given that Asians store more of their fat as visceral fat, this number is lower for Asians. The International Diabetes Federation guidelines suggest that a WC >35.4 inches for a man and >31.5 inches for a woman should raise suspicion for elevated visceral fat in Asians (Chinese, Japanese, and South Asians).

A more precise quantification of visceral fat can be done with a DEXA scan. Like a coronary artery calcium scan, this test involves a very low dose of radiation, costs $100-200, takes about 5 minutes, and does not require a prescription. Less than 1.7 pounds of visceral fat for women over 40 yrs old and less than <2.2 pounds of visceral fat for men are considered low risk (reference).

How to lose visceral fat

The good news is that all the things we know about weight loss will help with visceral fat loss as well. The basic principle is to sustain a small caloric deficit. Strategies for this include stopping eating after dinner, which for me reduced junk food consumption (let’s be honest, most of us typically do not eat healthy foods after 7pm). Reducing ultra-processed foods can be helpful as these foods are often high in calories and circumvent our satiety signals. Adequate protein and fiber can help with satiety. Eliminating alcohol can reduce visceral fat

High intensity interval training (HIIT) once a week can accelerate fat loss. This review of 79 randomized controlled clinical trials found that HIIT was superior for fat loss than moderate intensity continuous exercise - including just one 15 minute session per week. For me this involves one session per week of running for 3 minutes on the track followed by 3 minutes of rest - repeated for 3-4 rounds. This helps with both fat loss and improving VO2 max. I would also recommend strength training 2-3 times a week to minimize muscle loss.

Finally, get 7+ hours of sleep. Sleep deprivation elevates cortisol, which increases visceral fat. Being well rested also means you will make better decisions about food.

The curse of being South Asian

We know that visceral fat is toxic to our health. We know that Asians, particularly South Asians, store more of their fat as visceral fat. Even with a normal BMI, Asians can have excess visceral fat. I would advise getting a DEXA scan, especially for South Asians, so you can quantify your visceral fat - with a goal of under 2 pounds. Don’t settle for being skinny fat. Skinny fat can be very unhealthy.