#27. Body Fat Monday, August 16, 2021 Squishy fat. It loiters inside all of us. And it gets a pretty bad rap. As though it doesn't belong there. Like a homeless person. Have you ever sat at a red light and watched the driver ahead of you berate a nearby panhandler? Or perhaps it was you who did the lambasting (in your defense, he was an able-bodied twenty-something wearing unblemished Nikes, I know.) That's the level of respect we give to our fat. It just sits there, all day, doin' nothin'! "Get a job!", we yell at our flabby glutes, flapping triceps, and pumpkin-shaped bellies. "Yer all the same, ya' bunch a' good-for-nothin's!" That's a little bit unfair. Probably to the homeless person and definitely unfair to your adipose (i.e., fat), which is a complex and often misunderstood tissue. It's not just a chunky famine fund. Nor is it "all the same"; body fat is pretty diverse in both appearance and behavior. Some of it is white, some is beige, some is brown, and every color serves an important role in health and our maintenance of it (Bornstein et al., 2000; Carriere et al., 2014; Zoico et al., 2019). It is much fairer to characterize body fat as an endocrine organ: it secretes hormones and other signaling proteins, and has important roles in metabolism, reproduction, and immune function (Bornstein et al., 2000; Kershaw et al., 2004). White adipose tissue (WAT) is the variety that comes to mind when we get on a treadmill or do a truffle shuffle. It dwells in subcutaneous (just under your skin) and visceral (around your organs) regions, provides insulation, and acts as a major energy reserve, ready to release fatty acids when needed (Choe et al., 2016; Cohen et al., 2016). Brown adipose tissue (BAT) resides in proximity to critical organs and along vasculature, as well as subcutaneously around areas such as the axilla (armpit), neck, and clavicles (Sacks et al., 2013). It has more mitochondria, a greater vascular supply, and more sympathetic nerve innervation than WAT (Rosell et al., 2014). It's also critical for non-shivering thermogenesis. If you're cold, BAT comes to the rescue, burning up your energy to release heat (Cohen et al., 2016; Giralt et al., 2013; Szentirmai et al., 2017); this function could help us address obesity and the metabolic diseases associated with it (Wibmer et al., 2021). Good news: WAT can turn into BAT. Or something quite like it. The resulting cells are commonly referred to as beige (Nedergaard et al., 2014). Sympathetic activation, chronic cold exposure, exercise, and dietary interventions may exert a browning effect on our WAT (Nedergaard et al., 2014; El Hadi et al., 2019; Kaisanlahti et al., 2019). That's enough talk about our squishies for one day. Let's get to the tips: Tip 1) It's helpful to know your starting point. Approximately how much fat does your body currently have? Mirrors and bathroom scales can be deceiving. Circumferences (waist, hip, waist-to-hip, etc.) offer a little bit more information, and provide another mode of tracking progress. The same can be said for calipers: they aren't ideal for estimating total body fat, but they do a good job of assessing localized subcutaneous fat, and you can effectively assess change by measuring those same sites over time. Bioelectrical impedance devices are cheap, common, noninvasive, and they quickly report a total fat percentage. But that value tends to be inaccurate, and susceptible to wild fluctuations with food, hydration, exercise, and even skin temperature (Lukaski et al., 1986; Kushner et al., 1996; Slinde et al., 2001; Dehghan et al., 2008). Better alternatives exist: hydrostatic weighing, BOD POD, Fit3D, CT, DEXA, MRI, etc. (Snijder et al., 2006; Baum et al., 2016; Heymsfield et al., 2018; Ng et al., 2016). If you're using DEXA or MRI, you'll get an accurate number. But any mode (or combination of modes) can give you an approximate starting point, and if used periodically, can provide an objective assessment of any changes that may have otherwise been invisible. Or overestimated. Tip 2) Once you know what your percentage is (give or take), it's time to decide what you want it to be. "Lower! Way, way lower!" is usually the answer, but the best goal is to have a healthy amount. Remember: fat behaves as an endocrine organ, contributing to numerous essential processes. Body fat percentages exceeding 30% for women and 25% for men are considered obese, and are associated with an increased risk of cardiometabolic diseases (Kim et al., 2013). Contrastingly, extremely low body fat contributes to its own complications: immunity, reproductivity, bone density, etc. (Ziomkiewicz et al., 2008; Ravn et al., 1999; Demas et al., 2003). The American College of Sports Medicine publishes healthy ranges between sexes and across age groups. In their Guidelines for Exercise Testing and Prescription (Chapter 4), male values can be found on page 73 and females on page 74. It is important to note that women are not recommended to go below 10-13%, while men are capable of entering single digits without experiencing the same risk. On the upper end, however, women are a bit safer than men. Locate where you currently reside on those tables, and then choose a goal percentage that is healthy and realistic for your age and sex. Tip 3) You've figured out your current percentage. You've selected a goal. How fast should you accomplish it? What is a healthy rate of fat loss? Let's begin with what a healthy rate isn't: reality television in which huge bodies shed half their weight in a season. This is harmful to the individual as well as the public perception of weight management. Notice the shortage of reunions, in which the contestants return to showcase how much weight they kept off. And weight cycling (i.e., "yo-yo dieting") may associate with worse consequences than the embarrassment of the rebound (Montani et al., 2015). It is prudent to pace yourself no faster than 1-2lb each week (Finkler et al., 2012). Haste is not an efficient escort to your ideal body (Burne et al., 2012); patience is much more reliable.