Ray Peat's Anti-Fasting Position Reconsidered: Where T2 Changes the Argument

This post is a companion to the bioenergetic case for strategic fasting, which examined how exogenous T3 replacement modifies Ray Peat's cortisol-antagonism argument against fasting. That post focused on the T3 side of the question: when T3 is arriving from an external source, the specific deiodinase-mediated mechanism through which Peat argued fasting was metabolically counterproductive no longer functions the same way. The argument there is about the T4→T3 conversion bottleneck and why supplementing past it changes the fasting calculus.

This post has a different focus. The entire bioenergetic research framework treats mitochondrial function as the metabolic floor - the non-negotiable baseline beneath which no amount of hormonal optimization can compensate. And within that framework, 3,5-diiodothyronine (3,5-T2) is the direct mitochondrial-activator molecule: not a prohormone, not a nuclear receptor ligand, but a compound that binds cytochrome c oxidase (Complex IV of the mitochondrial electron transport chain) directly and acutely elevates aerobic respiration in a way that T3's genomic mechanism cannot replicate. Fasting paired with T2 supplementation is, on close mechanistic examination, a coherent combination that addresses the mitochondrial pathway from two distinct angles simultaneously. This combination is one that Peat could not have addressed directly, because the T2 literature as it now stands post-dates his major writings on fasting.

The argument developed here is not that Peat was mistaken about fasting's cortisol consequences. It is that the bioenergetic framework has a new input - the 3,5-T2 direct mitochondrial activation mechanism - that was not available to Peat when he formed his anti-fasting position, and that this new input changes the argument in a specific and mechanistically coherent way.

Research framing. This article reviews the Ray Peat anti-fasting position and 3,5-T2 mitochondrial mechanisms from a research-context standpoint. All compounds discussed are sold strictly for laboratory research and not for human consumption. See our /faq#legality page for full terms.

Quick Recap: What Peat Actually Said About Fasting

Ray Peat's opposition to fasting was not a vague aesthetic preference - it was built on a specific and mechanistically coherent chain of reasoning. The full elaboration is in the companion post, but the core argument deserves careful restatement here before the T2 angle is introduced, because the point is not to dismiss what Peat argued but to identify exactly where the T2 mechanism interacts with it.

Peat's argument ran as follows. Fasting depletes liver glycogen and drops blood glucose below the threshold at which dietary intake sustains it. The hypothalamic-pituitary-adrenal (HPA) axis responds by releasing cortisol, glucagon, and adrenaline. Cortisol's role in Peat's framework was not merely as a stress signal - it was as a direct metabolic suppressor via its action on the type 1 deiodinase enzyme (DIO1). Cortisol inhibits DIO1, the enzyme responsible for T4→T3 conversion, and simultaneously promotes the shunting of T4 toward inactive reverse T3 (rT3) rather than active T3. The net result: fasting reduces circulating T3 in proportion to how much the research subject depends on endogenous DIO1-mediated T3 production.

For the typical chronic-illness research subject in the population Peat was addressing - euthyroid or subclinical-hypothyroid, no exogenous T3, relying on their own thyroid-deiodinase axis for T3 availability - this chain was genuinely problematic. These subjects were already characterized by suppressed metabolic rate, marginal T3 availability, and elevated baseline cortisol from chronic stress. Adding a further cortisol load from fasting, in Peat's framework, pushed a population already at the edge of metabolic compensation further toward metabolic suppression.

Peat's argument is strongest precisely in this context: the euthyroid or untreated hypothyroid baseline, no exogenous T3 supplementation, and a normally functioning HPA axis responding to a caloric deficit. It weakens - and this is the thesis of both companion posts - when the T3 input condition changes. A research subject on sustained-release T3 replacement has a T3 supply that is not gated by DIO1 activity; the cortisol produced by fasting cannot suppress what the thyroid-deiodinase axis is not responsible for producing. The companion post develops this argument for the T4→T3 step in full. The current post adds the T3→T2 step, which is where the mechanism becomes genuinely novel and where the literature most clearly post-dates Peat's anti-fasting writings.

For the full treatment of why T3 replacement changes the cortisol-fasting calculation in the bioenergetic framework, see the bioenergetic case for strategic fasting.

What Peat's Framework Did Not Address: Direct Mitochondrial Activation

The 1994 paper by Goglia and colleagues - "Identification of 3,5-diiodothyronine binding sites in isolated rat liver mitochondria" - established a mechanism that sits outside the nuclear thyroid hormone receptor model that structured most of the relevant endocrinology literature through Peat's most productive writing decades. The finding: 3,5-T2 (3,5-diiodothyronine) binds directly to subunit Va of cytochrome c oxidase (Complex IV), the terminal enzyme of the mitochondrial electron transport chain, and acutely elevates aerobic respiration. The mechanism is non-genomic and rapid - operating in minutes rather than the hours-to-days time course of T3's nuclear receptor effects. And it is independent of the thyroid hormone nuclear receptors (TRalpha and TRbeta) through which T3 acts, meaning it represents a genuinely distinct mitochondrial-activation signal.

This distinction matters for understanding what Peat's framework does and does not address. Peat's T3 arguments are built around the nuclear receptor mechanism: T3 binds TRalpha and TRbeta, which then regulate the transcription of genes encoding mitochondrial proteins including the subunits of cytochrome c oxidase. Over days to weeks, this genomic action builds mitochondrial capacity by increasing the expression of electron transport chain enzymes. It is a structural, capacity-building effect operating through genetic regulation. What T3 does not do - and what the Goglia 1994 mechanism documents - is act directly and acutely on the cytochrome c oxidase enzyme already present in the cell. That direct, non-genomic, subunit-Va-binding activation is what 3,5-T2 provides.

The bioenergetic research community has only in the last decade begun to integrate 3,5-T2's role as a distinct mitochondrial-activating signal into the framework that Peat established. The basic cytochrome c oxidase binding was established in 1994, but characterization of 3,5-T2 as a physiologically relevant and independently supplementable compound with therapeutic research potential - distinct from the T3 framework rather than simply derivative of it - has developed substantially more recently. This is not a criticism of Peat's framework; it is an acknowledgment that the literature post-dated his major writings on fasting, and that the framework has a genuine gap at this specific mechanistic point.

For the full mechanistic detail on 3,5-T2, its cytochrome c oxidase binding properties, and how it differs from T3 at the cellular level, see the complete guide to 3,5-T2.

The T3→T2 Conversion Problem

To understand why the T2 mechanism matters for the fasting argument specifically, it is necessary to understand the deiodinase conversion chain and where it breaks down in the chronic-illness research population.

The type 1 deiodinase enzyme (DIO1) operates at two steps in the thyroid hormone conversion sequence. The first step is T4→T3: DIO1 removes one iodine atom from the outer ring of thyroxine (T4) to produce the active triiodothyronine (T3). This step is the one Peat focused on - the one that is impaired by selenium deficiency, elevated cortisol, and inflammatory cytokines, and that the bioenergetic framework bypasses with direct T3 supplementation. The second step is T3→T2: DIO1 removes another iodine atom, this time from the inner ring of T3, to produce 3,5-diiodothyronine (3,5-T2). This step uses the same enzyme, depends on the same cofactors (particularly selenium), and is suppressed by the same inflammatory and cortisol-driven impairments.

The T3→T2 conversion problem - documented in the research literature cited in the T3-to-T2 conversion problem and deiodinase dysfunction guide - is a two-step bottleneck for research subjects with deiodinase dysfunction. These subjects are not making enough T3 from T4; that is the first bottleneck that Peat's framework correctly identified and that T3 supplementation bypasses. But those same subjects are also not making enough T2 from whatever T3 they do have - because the same DIO1 impairment that blocks T4→T3 also blocks T3→T2. A research subject supplementing T3 and relying on endogenous DIO1 to convert some fraction of that T3 to 3,5-T2 may be providing adequate T3 for nuclear receptor signaling while leaving the cytochrome c oxidase-direct pathway substantially underactivated.

This is the mechanistic explanation for what the bioenergetic research community describes as the T3 protocol plateau: serum T3 that appears adequate, and yet metabolic markers stall. The T3 is doing its nuclear receptor job - driving mitochondrial enzyme transcription, upregulating the expression of electron transport chain proteins - but the cytochrome c oxidase-direct activation signal that requires 3,5-T2 is not being adequately supported because the DIO1 enzyme that would produce T2 from the supplemented T3 is the same enzyme that was impaired to begin with.

The full deiodinase dysfunction picture, including the two-step bottleneck and the plateau pattern, is analyzed in depth in the T3-to-T2 conversion problem and deiodinase dysfunction guide. The practical implication for the fasting argument follows directly: fasting's cortisol elevation further suppresses DIO1, meaning that a research subject who was already not producing adequate T2 from their supplemented T3 will produce even less T2 during a fasting window. This is an additional argument for direct T2 supplementation in the fasting-paired bioenergetic protocol - an argument that builds on the T3 replacement logic rather than replacing it.

Why Fasting + T2 Supplementation Is Mechanistically Coherent

The mechanistic case for combining fasting with T2 supplementation comes from recognizing that the two interventions target different stages of mitochondrial function - specifically, the creation of new mitochondria versus the activation of existing ones.

Fasting drives mitochondrial biogenesis. The signal runs through AMPK (AMP-activated protein kinase), which is activated when cellular energy status falls during caloric restriction, and through SIRT1 (sirtuin 1), which is activated when the cellular NAD+/NADH ratio rises during the shift away from glycolysis that fasting produces. Both AMPK and SIRT1 converge on PGC-1alpha (peroxisome proliferator-activated receptor gamma coactivator 1-alpha), the master transcriptional regulator of mitochondrial biogenesis. The documented result in the experimental literature [PMID: 16607139] is an increase in mitochondrial number per cell and mitochondrial density per unit of tissue - more electron transport chain complexes per cell, including more cytochrome c oxidase complexes. This is a structural capacity effect: fasting, over repeated cycles, builds a larger mitochondrial pool.

3,5-T2 activates the existing mitochondrial pool. The Goglia 1994 cytochrome c oxidase subunit Va binding is a non-genomic, rapid-acting mechanism that directly drives aerobic respiration in the mitochondria currently present in the cell. It does not create new mitochondria; it drives the existing cytochrome c oxidase complexes to operate at a higher rate. This is a functional activation effect, operating over minutes rather than the days required for biogenesis.

The combination is conceptually coherent precisely because the two mechanisms do not overlap. Fasting produces more cytochrome c oxidase complexes per cell through biogenesis. T2 supplementation activates those cytochrome c oxidase complexes directly and acutely. A research subject combining strategic fasting (biogenesis) with T2 supplementation (activation) is addressing the mitochondrial pathway at two distinct stages simultaneously: structural capacity through biogenesis, and acute functional activation through T2's cytochrome c oxidase binding. Neither intervention accomplishes what the other accomplishes, and the two together produce a more complete mitochondrial-targeting effect than either alone.

For research reference, the Wilson's T3+T2 Combo provides both T3 (for nuclear receptor signaling and as the substrate for endogenous T2 production) and 3,5-T2 (for direct cytochrome c oxidase activation) in a sustained-release formulation.

SR-T3 + T2 + Strategic Fasting: The Modified Bioenergetic Stack

The modified bioenergetic stack that the chronic-illness.st research position arrives at integrates three distinct and mechanistically complementary layers: sustained-release T3, direct T2 supplementation, and strategic fasting.

The thyroid hormone substrate layer - SR-T3 combined with T2 - addresses the deiodinase conversion bottleneck at both steps. The Wilson's SR-T3 Combo provides sustained-release T3 that bypasses the T4→T3 conversion bottleneck by delivering T3 directly, without dependence on the DIO1-mediated conversion that is impaired in the chronic-illness population. The Wilson's T3+T2 Combo extends this approach by adding 3,5-T2 directly, bypassing the T3→T2 conversion bottleneck in the same way that T3 supplementation bypasses the T4→T3 bottleneck. Together, these address the two-step deiodinase failure: the research subject receives T3 for nuclear thyroid receptor signaling and T2 for direct cytochrome c oxidase activation, without dependence on the DIO1 enzyme that is impaired in both conversion steps.

The strategic fasting layer adds two mechanisms that the thyroid hormone substrate layer does not provide. First, mitochondrial biogenesis: the AMPK/SIRT1/PGC-1alpha signaling cascade driven by caloric restriction increases the number of mitochondria per cell, expanding the structural capacity for oxidative phosphorylation. This is a structural investment that accumulates over repeated fasting cycles and compounds with the mitochondrial-capacity effects of T3's nuclear receptor signaling. Second, autophagy: the AMPK/mTOR/ULK1 pathway drives cellular clearance of damaged organelles and proteins, including the dysfunctional mitochondria that have accumulated from years of PUFA-driven lipid peroxidation and inflammatory damage. The cell-renewal cycle that mitophagy provides is complementary to the structural investment of biogenesis - clearing the damaged before expanding the new.

The full combined stack therefore targets thyroid hormone signaling (T3 nuclear receptor), mitochondrial creation (fasting-driven biogenesis via PGC-1alpha), mitochondrial activation (T2's cytochrome c oxidase binding), and cellular clearance (fasting-driven autophagy and mitophagy) simultaneously. Each element addresses a distinct mechanism; none replaces the others. This is the research-context framework that follows from treating the bioenergetic research community's work as an evolving body of mechanistic reasoning rather than a fixed orthodoxy. Both the SR-T3 and T3+T2 arms of this stack are available through the Wilson's T3+T2 Combo and Wilson's SR-T3 Combo respectively.

Where Peat's Argument Still Holds

The bioenergetic research community's evolving position on fasting is not a wholesale rejection of Peat's reasoning - it is a context-specific modification. Recognizing where Peat's argument retains its full force is as important as identifying where the T2 mechanism changes it.

For research subjects without exogenous T3 replacement, Peat's cortisol-antagonism argument remains fully valid. The mechanistic chain he identified - fasting elevates cortisol, cortisol suppresses DIO1, DIO1 suppression reduces T3 - depends on the research subject relying on endogenous T3 production. That dependence is the condition under which the chain operates. A subject not receiving exogenous T3 is exactly the population Peat was addressing, and for that population his reasoning has not been refuted. The T2 angle only further compounds the problem for unsupplemented research subjects: if DIO1 is already functioning suboptimally, fasting's additional cortisol-driven DIO1 suppression reduces both T3 availability and T2 availability simultaneously.

For research subjects with unstable thyroid status - where T3 dosing has not reached stable serum levels, where the rT3:fT3 ratio remains elevated, or where the HPA axis is still in active dysregulation - the protective mechanism that changes the fasting calculus is not yet operational. The argument for strategic fasting being compatible with T3 replacement depends on the T3 replacement being stable and effective. Research subjects still in the process of establishing that stability are, in the community's reasoning, in the same position as unsupplemented subjects for this purpose: the protective mechanism they would need in place is not yet there.

For research subjects with severe HPA dysregulation - blunted or inverted cortisol diurnal pattern, adrenal fatigue presentations, or low-baseline cortisol - fasting may exacerbate stress-axis dysfunction regardless of T3 status. Peat's concern about adding cortisol load to an already-stressed HPA axis applies even when T3 is being exogenously replaced, because the T3 replacement changes the deiodinase arm of the cortisol consequence without fully addressing the HPA axis burden itself. This is a context where the orthodox Peat position on fasting remains a more conservative and prudent framework than the modified-Peat position.

Peat's anti-fasting argument is not wrong. It is context-dependent. The context in which it holds with full force is the unsupplemented, unstable, or HPA-dysregulated research subject. The context in which the T2 mechanism most clearly modifies the argument is the research subject with stable exogenous T3, direct T2 supplementation, and sufficient HPA stability to tolerate a modest cortisol increase during the fasting window.

The Modified-Peat Position

This cluster follows Peat on the foundational elements that distinguish the bioenergetic framework from mainstream endocrinology and from conventional metabolic-health approaches. Thyroid hormone is the metabolic keystone, and T3 specifically - not T4, not a TSH target - is the operationally relevant compound. Anti-serotonin tooling, principally cyproheptadine, is a mechanistically coherent and underutilized intervention that the bioenergetic framework identified ahead of mainstream recognition. The anti-PUFA argument, built on lipid peroxidation's documented effects on mitochondrial membrane integrity and cardiolipin, is mechanistically sound. Pregnenolone and progesterone as mitochondrial protectors and anti-cortisol agents have meaningful peer-reviewed support. These positions are retained without modification.

The modifications are two and specific. First, on fasting: the anti-fasting position is correct for unsupplemented research subjects, but T3 replacement materially changes the calculation. The companion post develops this for the T4→T3 step; this post develops it for the T3→T2 step and the direct cytochrome c oxidase mechanism. The conclusion is that strategic fasting is compatible with an adequately supported bioenergetic protocol - specifically, with stable exogenous T3 and direct T2 supplementation in place. Second, on T2: the 3,5-T2 direct mitochondrial activation mechanism was not available to Peat as a supplementation target because the literature post-dated his major fasting writings. It represents a genuine mechanistic advance beyond what the T3 framework alone provides, and the bioenergetic research community's integration of it is not a contradiction of Peat's framework but an extension of its core logic: bypass the conversion bottleneck, deliver the active mitochondrial-targeting compound directly.

The result is a research-context framework that treats the original Peat protocol as a foundation, not a fixed orthodoxy. Peat's foundational mechanistic insights remain structurally sound; the framework they established has room for new mechanism as the relevant literature develops.

What Research Has and Hasn't Established

Established:

3,5-T2 binds cytochrome c oxidase at subunit Va - established by Goglia et al. 1994 [PMID: 8194599] and replicated in subsequent mitochondrial-physiology research. DIO1 produces 3,5-T2 from T3 through inner-ring deiodination - this is documented in the deiodinase enzyme literature [PMID: 15823294] and is the same enzyme family that produces T3 from T4 in the outer-ring deiodination step. Fasting drives mitochondrial biogenesis through the AMPK/SIRT1/PGC-1alpha axis - documented in the caloric restriction literature [PMID: 16607139] with cell-biology resolution and animal-model longitudinal data. Cortisol response to fasting is well-characterized in euthyroid subjects [PMID: 3791672], and the cortisol-DIO1 suppression link is documented in the thyroid-cortisol axis research. DIO1 impairment in chronic illness and inflammatory states affects both the T4→T3 and T3→T2 conversion steps.

Hypothesis:

The modified-Peat framework combining SR-T3 + T2 supplementation (via the Wilson's T3+T2 Combo) + strategic fasting produces better mitochondrial outcomes than the orthodox Peat anti-fasting protocol in research subjects with DIO1 deiodinase dysfunction. This hypothesis is mechanistically coherent: the component mechanisms (T3 nuclear receptor signaling, T2 cytochrome c oxidase activation, fasting-driven biogenesis, fasting-driven autophagy) are individually supported in the research literature, and their combination addresses the mitochondrial pathway at distinct and non-overlapping stages. The integrated hypothesis has not been validated in a randomized controlled trial of chronic-illness research subjects and sits in the category of research-community mechanistic theory.

Not endorsed by mainstream endocrinology or the orthodox Ray Peat community:

This is a research-community position from a specific subset of the bioenergetic research community. Mainstream endocrinology does not endorse exogenous T3 supplementation for most thyroid presentations, does not endorse T2 supplementation as a recognized intervention, and does not endorse the modified-Peat framework developed here. The orthodox Ray Peat community has not broadly adopted the T3-replacement-changes-the-fasting-calculus framing, continues to hold Peat's anti-fasting position as foundational, and has not integrated T2 supplementation as a protocol element. The position developed in this post is a minority position within the bioenergetic research community - grounded in mechanism, not backed by the clinical-trial evidence that would be required for mainstream acceptance.

Frequently Asked Questions

Did Ray Peat oppose all forms of fasting?

Peat's opposition to fasting was consistent and covered multiple formats - intermittent fasting, time-restricted feeding, and extended caloric restriction all fell under his critique. His mechanistic argument was not specific to the length of the fast but to the cortisol-DIO1-T3 chain that caloric restriction triggers whenever liver glycogen depletes and blood glucose drops below the level dietary intake can maintain. The bioenergetic community's modification of this position - specifically, that T3 replacement changes the calculus - applies differently to different fasting patterns, with shorter time-restricted feeding windows generating a more modest cortisol response than extended fasting. Peat did not distinguish between these patterns in terms of the underlying mechanism he was concerned about, but the magnitude of the cortisol response does vary with fasting duration in the research literature.

What is 3,5-T2 and why does it matter for the fasting argument?

3,5-diiodothyronine (3,5-T2) is a downstream metabolite of T3 deiodination produced by the DIO1 deiodinase enzyme. Unlike T3, which acts primarily through nuclear thyroid hormone receptors (TRalpha and TRbeta) to regulate gene transcription over hours to days, T2 binds directly to subunit Va of cytochrome c oxidase (Complex IV of the mitochondrial electron transport chain) and acutely drives aerobic respiration in a non-genomic, minutes-scale mechanism. For the fasting argument, T2 matters because: fasting's cortisol elevation suppresses DIO1, which would ordinarily be converting supplemented T3 into T2; and fasting drives mitochondrial biogenesis (more cytochrome c oxidase complexes per cell), which is the structural substrate that T2 activates directly. Direct T2 supplementation bypasses the DIO1 bottleneck and pairs directly with fasting-driven biogenesis in a mechanistically coherent way.

How does T3 to T2 conversion connect to fasting?

The T3→T2 conversion step uses the DIO1 enzyme, the same enzyme that converts T4→T3. During fasting, cortisol elevation suppresses DIO1 activity, which means both conversion steps are impaired simultaneously. A research subject who supplements T3 but relies on endogenous DIO1 to produce T2 from that T3 faces a specific problem during fasting: the cortisol produced by caloric restriction further reduces the DIO1 activity that was already impaired, leaving the cytochrome c oxidase-direct pathway (which requires T2) even less supported during the fasting window. This is documented in detail in the T3-to-T2 conversion problem and deiodinase dysfunction guide. The logical response is direct T2 supplementation - the same deiodinase-bypass logic that Peat applied to the T4→T3 step, extended one step further downstream.

Does the cortisol argument apply to research subjects on SR-T3?

The cortisol argument applies in a modified form. Cortisol elevation during fasting still suppresses DIO1, still promotes rT3 production from residual T4, and still reduces thyroid hormone receptor sensitivity at the tissue level. What changes for SR-T3 research subjects is the deiodinase-mediated T3 suppression specifically: the active T3 arriving from a sustained-release formulation is not gated by DIO1 activity, so cortisol's DIO1 inhibition does not reduce T3 availability the way it does for subjects relying on endogenous conversion. The cortisol argument therefore retains its receptor-sensitivity arm (cortisol still blunts tissue response to T3) but loses its most consequential mechanism (the T3 supply reduction) for adequately T3-supplemented research subjects. This is a partial neutralization, not a complete dismissal of cortisol's fasting-state effects.

What is the modified-Peat fasting position?

The modified-Peat position holds that strategic fasting is compatible with the bioenergetic protocol for research subjects who have stable exogenous T3 and direct T2 supplementation in place. Peat's anti-fasting argument is acknowledged as correct for unsupplemented research subjects in the context he was addressing. The modifications are: first, T3 replacement removes the most consequential mechanism in Peat's chain (DIO1-mediated T3 suppression by fasting-cortisol); second, T2 supplementation addresses the further DIO1-mediated T2 suppression that fasting's cortisol elevation would otherwise cause; and third, fasting's AMPK-driven mitochondrial biogenesis creates the structural substrate that T2's cytochrome c oxidase activation directly targets. The result is a framework where fasting and the thyroid hormone substrate stack are mechanistically complementary rather than conflicting.

Should T2 supplementation be paired with fasting?

From a mechanistic standpoint, the pairing is coherent. Fasting drives mitochondrial biogenesis (more cytochrome c oxidase complexes per cell) while also suppressing DIO1 (reducing endogenous T2 production from supplemented T3). T2 supplementation activates the cytochrome c oxidase complexes that fasting's biogenesis produces, and bypasses the DIO1 conversion step that fasting's cortisol elevation impairs. The two mechanisms work at different stages of mitochondrial function (biogenesis vs activation) and address different parts of the deiodinase dysfunction problem (DIO1 impairment affecting T3→T2 conversion). Direct T2 supplementation during a fasting protocol is mechanistically distinct from relying on endogenous conversion - the distinction that makes the pairing coherent is the same bypass logic that applies to T4→T3. Whether a specific research subject should pair T2 with fasting is a context-dependent question that depends on their current thyroid status and other factors.

Is the Wilson's T3+T2 combo designed for use with fasting?

The Wilson's T3+T2 Combo is formulated as a sustained-release product delivering T3 and T2 together in a hydroxypropyl methylcellulose (HPMC) matrix. The sustained-release formulation is mechanistically well-suited to fasting contexts because it does not depend on food intake for absorption and produces a flat, stable serum curve through a fasting window - the same pharmacokinetic rationale that makes SR-T3 suited to fasting protocols. The combined T3+T2 formulation is designed to address both the T4→T3 and the T3→T2 conversion bottlenecks in a single product, and from that standpoint it is aligned with the modified-Peat fasting framework developed in this post: it provides the thyroid hormone substrate stack that changes the fasting calculus from the T2 as well as the T3 side.

Where does this position diverge from the Ray Peat community consensus?

The divergence runs on two axes. On fasting: the orthodox Ray Peat community continues to hold Peat's anti-fasting position as foundational and has not broadly adopted the T3-replacement-changes-the-calculus framing that the bioenergetic research community's evolving subset has developed. On T2: the orthodox Peat community does not integrate 3,5-T2 supplementation as a protocol element - the T2 literature post-dates Peat's major writings, and the community that formed around his work has not systematically incorporated this newer mechanistic layer. This post's position is that both divergences are extensions of the same deiodinase-bypass logic that Peat applied to the T4→T3 step, carried one step further downstream and applied to a fasting context he could not have addressed with the literature available to him.

Closing Note

The T2 mitochondrial mechanism is the missing layer in Ray Peat's anti-fasting argument - not a refutation of it, but a genuine addition that the literature could not have provided during Peat's most productive writing years. The bioenergetic framework he established, with T3 as the metabolic keystone and mitochondrial function as the metabolic floor, points directly toward this extension once the 3,5-T2 cytochrome c oxidase mechanism is incorporated. For the full research-community context, see the Ray Peat protocol complete 2026 research guide. For the reference compound product that addresses both the T3 and T2 arms of the modified stack, see the Wilson's T3+T2 Combo. The complete bioenergetic-framework research product stack is available in the catalog.