Newsletter #287: Zinc, Selenium, & Metabolism 🔥
When you go through nutritional literature, an apparent paradox emerges: People with obesity very commonly have inadequate levels of various nutrients, despite obviously consuming more calories than counterparts with a healthy body mass.
Why this is the case remains unclear. In some cases, it may be due to poor diet quality even in the context of overnutrition (ultra-processed foods generally aren't noted for being nutrient-rich). But obesity may also affect bioavailability and metabolism of certain nutrients, making them more vulnerable to nutrient gaps.
This is particularly a concern during weight loss, since reduced food intake can escalate deficiencies.
Interestingly, recent research suggests that higher levels of some of these nutrients may be inversely associated with obesity. Does this mean that restoring these nutrients through supplementation could improve fat burning?
This Week’s Research Highlights
Lower levels of certain antioxidants – including zinc and selenium – are associated with body fatness.
Individuals with overweight/obesity tend to have lower blood concentrations of key nutrients, particularly dietary antioxidants. To examine the available evidence that explore this association, researchers in Australia performed a systematic review and synthesized data from 31 studies.
Their analysis revealed that circulating levels of carotenoids and vitamin E were both associated with lower body fatness. However, both of these compounds are fat-soluble, so it's possible that individuals with greater fat mass are sequestering more of the nutrients into storage, thus leaving less to hang around in the bloodstream.
They also determined that higher vitamin C status is associated with lower body fatness. Here too, we encounter a complication, since vitamin C is water soluble, and differences in water balance due to obesity makes it hard to interpret why exactly serum levels of vitamin C might differ.
Finally they looked at various minerals. Results here were inconsistent, but generally suggested that lower serum levels of zinc, magnesium, and selenium were associated with obesity. Notably, greater body fatness in childhood when accompanied with zinc deficiency was linked to higher risk of obesity in adulthood.
Importantly, most of the studies examined in this review were cross-sectional – meaning that they were measuring either intake or status of these antioxidants in these people at a single point in time. That makes it pretty hard to tell whether the levels of antioxidants were driving obesity, or if obesity was leading to differences in antioxidant status.
That's why intervention studies – like the one described below – are key for establishing the direction of causality.
Supplementation with zinc and selenium increases resting metabolic rate in people with overweight/obesity on a reduced calorie diet.
A prior systematic review found that people with obesity often have lower levels of zinc and selenium, and randomized trials show that supplementation with these minerals could favorably influence body composition, perhaps by altering thyroid hormones. However, the results were inconclusive due to limitations of the available literature.
To examine the effects of supplementation with zinc and selenium in the context of weight reduction, researchers in Cyprus recruited 28 adults with a BMI above 25 (mean BMI was ~29).
Participants were randomly split into either a placebo group, or supplementation with 40 mg/day of zinc and 400 mcg/day of selenium. A registered dietitian consulted with them and devised balanced reduced-calorie diets for each individual that was 300 calories lower than their current estimated energy requirement. Resting metabolic rate (RMR) was estimated using indirect calorimetry
After eight weeks, the RMR of the supplement group had risen from an average of 1923 up to 2364 -- that is an increase of 441 calories, or almost 23%! The placebo group, in contrast, experienced a modest reduction in their RMR (not statistically significant).
It was expected, based on prior research, that this might be due to thyroid function. However, the supplement group didn't show differences in thyroid hormone levels, indicating other mechanisms may be at play.
The researchers speculate that the metabolic benefits of selenium and zinc might be attributable to the well-established antioxidant effects of the two minerals, particularly in the context of obesity. Obesity is associated with an increase in reactive oxygen species. Oxidative stress, in turn, exacts a major toll on the mitochondria, which generate energy for our cells. Thus, it makes sense that restoring antioxidant defenses through these minerals might lead to healthier mitochondria, and in turn to increased energy expenditure.
Random Trivia & Weird News
Pennies in the US are copper-plated for appearance, but actually are zinc based. Consequently, swallowing coins can lead to dangerously high levels of the mineral (it’s probably not great for your health for other reasons, of course).
In one case study, doctors extracted an astounding 461 coins from the gastrointestinal tract of a patient. The coins suffered corrosion due to contact with gastric juices, exposing the person to massive levels of zinc throughout the body. They ultimately died with multi-system organ failure.
Podcasts We Loved This Week
- Danny Lennon & Alan Flanagan: The Big Unanswered Questions in Nutrition Science. Via Sigma Nutrition Radio (Congratulations on episode 500 to Danny and the team!)
- Debra Skene: The Effects of Shift Work on Health and Performance. Via Reason & Wellbeing Podcast.
Products We Like
Dan has been using this product for a while and is a huge fan. It contains all of the essential minerals in readily absorbable form and reasonable doses, so you’re not going to overdo it if you take this in conjunction with a balanced diet. Furthermore, Nordic Naturals is a highly legit brand that third-party tests all of their products, so you don’t have to worry about being scammed.
FYI — they also make a version without iron.
humanOS Catalog Feature of the Week
The course takes a deep dive into phytochemicals in plants, their powerful health effects, and how intelligently-devised smoothies can help optimize our intake of these compounds. Not only do smoothies provide a source of phytonutrients to the diet, but since well-composed smoothies are made from fruits and vegetables, they are a great source of essential vitamins and minerals.
For more practical information on using smoothies to enhance nutrition, please refer to our How-to Guide for smoothies.