Leisha Fat is an organ! Surprise!
Working with people has a wonderful way of sending me back into research. Someone comes along with an interesting health question, we start looking at what is happening inside their body, and I find myself learning something new. Our bodies are quite remarkable in the way they operate, but the science can become terribly complicated. I enjoy trying to decipher it and put it into ordinary language so that both I and the people I work with can understand what is going on.
My latest research adventure has been FAT! It began with someone eating considerably more animal fat, very few carbohydrates and feeling remarkably good. I wanted to understand what happens when our bodies change the fuel they are using, and how insulin, the thyroid, liver and intestinal microbes participate in the process. Somewhere along the way, I discovered that our fat tissue is actually considered an endocrine organ.
An organ! All this time we’ve been talking about eating fat, burning fat, avoiding fat and getting rid of fat, while this extraordinary living tissue has been busy manufacturing hormones, communicating with our brain, regulating energy and participating in our immune system. Apparently, we even have several different kinds of fat, each with its own particular job.
And then my soil-food-web brain took over, because I began wondering whether we have been looking at fat in much the same way that people look at dirt.
Fat is not dirt!
In the Soil Food Web world, we make an important distinction between dirt and living soil. When I use the word dirt in my teaching, I’m talking about material that has lost much of the biological activity and structure that make healthy soil function. Living soil is an entirely different world, containing bacteria, fungi, protozoa, nematodes, organic matter, minerals, water and an extraordinary network of relationships.
Compost is another beautiful example of this biology at work. Organic materials are transformed, nutrients are released and organisms reproduce, feed and interact. A healthy compost pile can become remarkably hot simply because so much biological activity is taking place inside it. What appears to be a pile of decomposing material is actually a rather busy living system.
Our fat tissue deserves a similar change in how we look at it. It isn’t simply a lump of stored calories sitting beneath our skin, waiting for us to burn it off. It contains blood vessels, nerves, immune cells and specialised fat cells that store and release energy while sending chemical messages throughout our bodies.
Healthy soil stores water and nutrients and releases them through biological processes when plants need them. Healthy fat tissue stores energy and releases it when our bodies require additional fuel. Both depend on their structure, their surrounding environment and the biological relationships taking place within them, though they are obviously very different kinds of living systems.
When soil becomes compacted or biologically depleted, nutrients and water may still be present, but their movement and availability can become disturbed. Something interesting happens when our fat tissue becomes metabolically dysfunctional, too. The energy reserves are still there and the cells are still alive, but the hormonal messages, inflammatory activity and release of fatty acids may no longer be properly regulated.
Our bodies need functioning fat tissue just as our gardens need functioning soil. Perhaps we have spent far too much time trying to get rid of fat without appreciating everything it does for us.
Meet the fat family
Our familiar white fat is the body’s principal energy reserve, and much of it sits beneath our skin. This subcutaneous fat insulates us, cushions our tissues and stores energy as triglycerides, which can be broken down and released when we need additional fuel. Healthy subcutaneous fat provides an important storage space, helping prevent excessive fat from accumulating inside our organs.
Then we have visceral fat, which lives deeper in our abdomen, surrounding our intestines and other internal organs. A normal amount belongs there, but excessive accumulation can interfere with metabolism. As fat cells enlarge, their surrounding environment can become stressed, immune cells begin responding and inflammatory signaling may increase, contributing to disturbances in insulin sensitivity and liver metabolism.
This is where the soil analogy becomes particularly interesting. A piece of land can contain plenty of nutrients yet be unable to cycle them properly because the structure and biological relationships have become damaged. Our bodies can also have plenty of stored energy while struggling to regulate how that energy is released, transported and used.
We have another situation called ectopic fat, where excessive lipids accumulate inside tissues such as the liver, pancreas and muscles. This is like nutrients accumulating in the soil where they aren’t needed while other parts of an ecosystem struggle to function. In our bodies, excessive fat inside these organs can interfere with normal cellular activity, particularly the processes involved in insulin signaling and energy regulation.
Next is brown fat that has a completely different job. Brown fat contains enormous numbers of mitochondria, those tiny energy-producing structures inside our cells, and it uses fatty acids and glucose to manufacture heat. Adults have brown fat around their neck, collarbones and upper spine, where it helps regulate body temperature.
Just like a heating compost pile, we have our own biological heating system, although the mechanisms are different. Compost generates heat through the collective metabolism of microorganisms, while brown fat uses a mitochondrial protein called UCP1 to release energy as heat. Our nervous system can activate brown fat when we are exposed to cold, drawing on available fuels to help keep us warm. This is where cold therapy (or hot and cold) becomes interesting but that is another topic.
Brown fat also has a cousin called beige fat. Beige fat develops within white-fat tissue and acquires some of brown fat’s heat-producing abilities. Researchers are investigating how these adaptable fat cells might contribute to metabolic health,.
Fat is talking to our brain, thyroid and pancreas
Our fat cells manufacture hormones called adipokines, including leptin and adiponectin. Leptin helps communicate our energy reserves to the brain, influencing appetite and energy expenditure, while adiponectin supports insulin sensitivity and the use of fatty acids for energy. These hormonal messages can change when fat tissue becomes stressed or metabolically dysfunctional, influencing other organs throughout the body.
Insulin is particularly important because it helps regulate whether incoming energy is being stored or used. After we eat, insulin encourages energy storage and slows the release of fatty acids from our existing reserves. Between meals, insulin generally falls, allowing stored fat to become available again for our muscles and other tissues. When somebody substantially reduces carbohydrates and increases dietary fat, their body generally begins relying much more heavily on fatty acids for energy. The liver may also produce ketones, providing another source of fuel. Interestingly, burning additional fat doesn’t automatically mean losing stored body fat, because we might simply be using the additional fat arriving from our meals.
The thyroid is also involved, particularly in energy expenditure, cholesterol metabolism and body temperature. Brown fat possesses an enzyme called DIO2, which converts T4 into the active thyroid hormone T3 within the tissue itself. This local thyroid hormone activity helps support the mitochondrial machinery responsible for producing heat.
Our thyroid, nervous system and fat tissue are communicating continually, and those relationships change according to our hormonal environment and energy requirements. Fat is involved in storing energy, responding to hormones and manufacturing hormones of its own, while the liver and pancreas help coordinate the whole process. It is a rather busy organ for something we’ve been treating as an unwanted storage compartment.
Microbes are involved, too!
Of course, I found myself back in the microbiome research, because our intestinal microbes participate in fat metabolism through several fascinating pathways. Our liver manufactures bile acids from cholesterol, which help us digest and absorb dietary fats. Some of these bile acids encounter microorganisms living in our intestines, where particular bacteria transform them into compounds with different biological properties. These compounds can also act as chemical messengers, influencing glucose regulation, liver metabolism and energy expenditure.
One bile-acid receptor, called TGR5, can activate pathways involving the same DIO2 enzyme that converts T4 into active T3. Experimental research has demonstrated connections between this signaling system and heat production in brown fat, although researchers are still investigating its practical significance in humans. Here we have our liver, intestinal microbes, thyroid hormone metabolism and fat tissue participating in a fascinating biological relationship.
Our microbes also transform some of the plant fibres and resistant starches we eat into short-chain fatty acids, including acetate, propionate and butyrate. Butyrate provides an important energy source for the cells lining our colon, while these microbial compounds also participate in immune regulation and influence intestinal hormones involved in appetite and insulin secretion.
The relationship works in several directions. What we eat influences the nutrients available to our intestinal microbes, those microorganisms produce compounds that communicate with our own cells, and our metabolic environment influences the conditions in which our microbes live. Scientists are investigating how these relationships affect white and brown fat, including the regulation of energy storage and heat production.
This makes me particularly interested in what happens when someone changes their diet dramatically. Eating considerably fewer carbohydrates may change insulin secretion and the fuels our body uses, while removing certain foods may also improve digestive comfort. Gradually bringing different plant foods back into the diet gives us an opportunity to observe how we respond while expanding the nutritional resources available to our intestinal microbes.
And, back to the garden
I am always looking to see the connections in nature. Is the health of the soil like the health of our microbiome.
What fascinates me about soil is that we cannot judge its biological function simply by looking at a pile of material. I want to know which organisms are present, how they are interacting, whether nutrients are cycling and whether the soil has the structure needed to hold water and support roots. A garden might have plenty of nutrients on paper and still be struggling because the living relationships have been disrupted.
I have created a protocol recently that I wrote about in my Plant & Kitchen Alchemy book. Cooked and cooled potatoes provide resistant starch, apples bring pectin, and our onions, garlic, chia and flax offer different fibres for our intestinal microbes to work on. The soil food web helps cycle nutrients for the plants we grow, and those plants eventually provide food for both our own cells and the microorganisms inhabiting our intestines.
I’m beginning to look at our fat tissue with a similar curiosity. How well is it storing and releasing energy? What hormonal messages is it sending? Is excessive fat accumulating around or inside organs, and how are our thyroid, insulin, liver and intestinal microbes participating in the process?
My latest research adventure began with a simple question about eating more fat and feeling better, and I’ve ended up with an entirely different appreciation for an organ that we have spent decades trying to shrink. Fat is living tissue with remarkable responsibilities, and its health involves considerably more than how much of it we carry.
Healthy soil holds and supports life. Healthy fat tissue helps store, distribute and regulate the energy that supports our own lives. Both have reminded me that the material we can see is only part of the story, and understanding the biology working within it changes everything. Who knew a conversation about FAT would bring me right back to the soil
Resources and references
For anyone interested in exploring the research, these publications cover the endocrine function of fat, brown and beige fat, and the connections between thyroid hormones, bile acids and our intestinal microbes. I strongly suggest watching Dr Li’s video.
Dr. William Li: Eat THIS to Burn Visceral Fat (YouTube)
https://www.youtube.com/watch?v=WQZgau7hmSg
Biochemistry of adipose tissue: an endocrine organ – PMC
https://pmc.ncbi.nlm.nih.gov/articles/3648822/
Uncovering the origins of brown fat | National Institutes of Health (NIH)
https://www.nih.gov/news-events/nih-research-matters/uncovering-origins-brown-fat
Gut microbiota in overweight and obesity: crosstalk with adipose tissue | Nature Reviews Gastroenterology & Hepatology
https://www.nature.com/articles/s41575-023-00867-z
Endocrinology of the Gut and the Regulation of Body Weight and Metabolism – Endotext – NCBI Bookshelf
https://www.ncbi.nlm.nih.gov/books/NBK556470/
Mechanism of action of the bile acid receptor TGR5 in obesity – PMC
https://pmc.ncbi.nlm.nih.gov/articles/PMC10840437/
