If you've been researching lignans for your dog's Cushing's syndrome or Cushing's disease, you've probably run into two terms: SDG lignans and HMR lignans. Both are used to manage Cushing's naturally. Both have a track record. And they're not the same thing.
Here's a plain-English breakdown of how they differ, when one has an advantage over the other, and what most owners end up choosing.
What SDG Lignans Are
SDG (secoisolariciresinol diglucoside) lignans are found in many plants, but are found in particularly high concentrations in flaxseed hulls — the outer layer that's removed when flaxseed is processed. Thus, most available SDG products are extracted from this source. They're the most widely studied form of lignans for canine Cushing's syndrome (including Cushing’s disease), and the dosing protocol most commonly cited by integrative veterinarians is built specifically around them: one (1) to two (2) mg of SDG lignans per pound of body weight, once daily.
When a dog digests SDG lignans, gut bacteria convert the lignans into active compounds (enterolactone (ENL or EL) and enterodiol (ENT or ED)) that interact with the hormonal system. This conversion step is one reason probiotics can enhance (and taking antibiotics can diminish) lignan effectiveness — healthy gut bacteria do more of the converting work. Conversion by gut bacteria (and absorption by the body) can be boosted even further by the addition of the pre-biotic inulin.
What HMR Lignans Are
HMR (7-hydroxymatairesinol) lignans come from the knots of Norwegian spruce trees. Dosing for HMR is the same as for SDG lignans: one (1) to two (2) mg of HMR lignans per pound of body weight, once daily.
How They're Similar
Both HMR and SDG lignans are converted into enterolignans in the gut of the animal. These enterolignans then influence the body's steroid hormone production by blocking enzymes that are essential for that production, thereby helping moderate cortisol overproduction as well as the production of other adrenal hormones involved in Cushing’s syndrome. Survey data from owners managing Cushing's naturally shows similar response rates between the two forms — approximately 85% of lignan users report improvement in at least one Cushing's symptom within two months, regardless of which type they used. Both are safe for long-term use and well tolerated.
How They're Different
The main practical differences:
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While both require gut bacteria to convert lignans into the biologically active enterolignans, SDG conversion (metabolism) requires a 3-step (for ED) or 4-step (for EL) process, while HMR metabolism involves only a 2-step process. Thus, the conversion of SDG can take longer and involve more types of bacteria (although the first step happens rapidly and is accomplished by a wide array of bacteria). This may be better or worse in any given case, as different animals may respond differently to this time-release effect of enterolignans in the case of SDG lignans
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SDG metabolism results in both types of enterolignans–ED and EL, whereas HMR metabolism can only produce EL. Thus, SDG lignans can provide a more broad-spectrum enterolignan approach. Both types are, in general, as effective, but in a given animal one or the other type might be better
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HMR is more directly bioavailable. However, an unfortunate consequence of this is that the lignans can be absorbed directly into the blood stream before they have had time to convert into enterolignans. Unconverted lignans are of no effect in blocking cortisol production. While there is still the possibility of subsequent metabolism (this has not been well studied), it is likely that some fraction of each HMR dose will be wasted. By contrast, researchers have found no unconverted SDG (or its first metabolite, SECO) in animal serum
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SDG carries a higher antioxidant load overall
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HMR comes from a different plant source, which matters if your dog has flaxseed sensitivities
Which Should You Choose?
For most dogs, either works just as well. However, if your dog doesn’t seem to be improving despite varying the dosage, adding probiotics (and the prebiotic inulin) and not being on antibiotics, then try the alternative source. If your dog is on antibiotics, HMR (along with probiotics and inulin) may have the advantage, as less bacteria and less time are involved in its metabolism.
Some owners use both. There's no known interaction, and the protocols complement each other, although you should keep the total dosing between the two to 1-2 mg/pound of body weight/day.
A Note on Atypical Cushing's
If your dog has been diagnosed with atypical Cushing's — the sex hormone-driven form rather than cortisol-driven — SDG lignans may have a specific advantage due to their broader-spectrum approach.
More on natural Cushing's management: Cushings In Dogs — Holistic Treatment Options
For a list of all our lignans products, click here.
Sources:
• University of Tennessee College of Veterinary Medicine — Treatment Considerations