Underweight, in Aajonus's framework, is not a cosmetic or aesthetic problem, it is a profound physiological deficit representing a fundamental lack of protective fat reserves, a scarcity of the single most important nutrient in a toxic industrial society. Being underweight means the body has insufficient fat to buffer, harness, absorb, and neutralize the constant stream of environmental toxins, chemical pollutants, heavy metals, and industrial poisons that every person living in a modern civilization encounters daily. It is not simply a matter of caloric deficit or low body mass, it is a condition in which the protective biological architecture of the body is compromised at its most foundational level.

Aajonus was emphatic that being underweight in a toxic environment is the most dangerous condition a person can be in, more dangerous than obesity. He stated clearly and repeatedly that skinny people in a polluted society are the sickest people he encountered, took the longest to reverse and heal, and always had to become the fattest, and stay the fattest the longest, during recovery. He said: "I'll show you the people who are ultra skinny. I mean bone thin with skin on bones. And those people are the sickest. And take the longest to reverse and get well, and always have to become the fattest. And stay the fattest the longest."

He defined underweight not merely as a number on a scale or a low BMI, but as a state in which the fat reserves of the body are insufficient to serve their protective, neurological, structural, and detoxification functions. On the Primal Diet, with raw meat increasing tissue density, what might appear as a normal or even slightly heavy weight on conventional charts may actually represent an underweight condition internally, because the conventional weight charts, Aajonus said, were made for cooked-food eaters and are entirely inaccurate for raw meat eaters.

He further clarified that being underweight is not simply about appearing thin. He personally carried 18.5% to 26% body fat at various points and appeared slender because raw fat molecules are very tiny, 10 to 50 times smaller than cooked fat molecules, which swell dramatically upon heating. So a person could look thin and actually be fat if they're eating raw fats, and conversely could look thin and actually be dangerously deficient in fat if they are eating cooked food or no fat at all.

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Aajonus identified multiple converging causes for the underweight condition, operating at the cellular, biochemical, dietary, and environmental levels.

Lack of fat in the diet and the inability to utilize fat: The body can only store and use fat that it receives. If a person is consuming little or no dietary fat, or is consuming cooked fat, which swells 10 to 50 times its normal size and becomes biologically burdensome rather than bioavailable, the body cannot build adequate fat reserves. Raw fat molecules, by contrast, are extremely small and can be deposited throughout the body efficiently.

Vegetarian and vegan diets: Aajonus pointed explicitly to vegetarianism as a root cause of underweight in multiple case studies. He described a woman who was on a vegetarian diet for fourteen years and did not get well. He described himself getting too thin when he "switched to all raw but meatless diets" and then bicycled and lived outdoors, the stress was so great that he deteriorated. He described a patient who was a vegetarian and was "skin on bone, lanky, frightfully" thin. He stated plainly: "If vegetarianism hasn't made you healthy in fourteen years, do you think that you're plagued with these problems for some spiritual or psychological reasons?" Plant fats, he explained, are made of larger molecules than animal fats and require an herbivore's digestive system to break them down, humans are not designed to efficiently extract and utilize plant fat, so vegetarians accumulate inadequate fat reserves.

Extreme physical exertion without adequate fat intake: Aajonus described himself becoming dangerously thin after two and a half years of bicycling and living outdoors on a raw but meatless vegetarian diet. Athletes who are trained to be thin and "ripped", gymnasts, runners, cyclists, are consuming their fat reserves and not replenishing them adequately. He noted that athletes who keep themselves at 7-8% body fat, which is considered the ideal in conventional athletic training, are actually drying out internally, burning out quickly, and most of them are done by age 38. He described gymnasts as burning out quickly, very few surviving past 32 in their careers, and said: "They're taught to be thin. They're taught to be ripped, unless you're a football player. What happens? They burn out young. 38 years old, their career's over."

Chronic disease, long-term illness, and systemic deterioration: Aajonus described a patient named Jeff Slay who deteriorated to approximately 68 pounds at 5'9.5", an Auschwitz-like appearance, he said. This patient had been told by conventional doctors that he was in "perfect health" based on blood markers. His underweight was a result of systemic breakdown, the inability of his cells to assimilate nutrients, and progressive wasting. He also described a woman who came to him with chronic fatigue beginning at age 14, who arrived at age 28 with breast cancer, cancer of the hip bone, and cancer of the kidney/adrenal gland: "Skinny. Skinny. 5'5". 18, 17, 16 days from birth. Very thin."

Toxins bypassing fat storage and damaging live cells: Because there is no fat buffer in an underweight person, environmental and dietary toxins, instead of being absorbed into fatty tissue where they do relatively little harm, go directly into the active living cells of the body and damage them. Once a cell is damaged by toxins, it is mutated, and it takes generations of cellular reproduction to re-educate and redevelop it into something healthy. This is why underweight people are so much harder to bring back to health than overweight people. Aajonus said: "I can always reverse toxic damage that's done when it's stored in fat. But when it's damaged the cell, that cell is mutated. And it takes generations to re-educate them and re-develop them into something healthy again."

Nervous system irritability from lack of fat: Without fat, every piece of environmental information, sensory stimulation, electromagnetic fields, chemical irritants, emotional stress, impacts the nervous system without buffering. The nervous system has no insulation. Aajonus described thin people as uniformly irritable, hyperactive, type-A, short-fused, never satisfied, manic, easily angered. He said that in his clinical experience, approximately 90% of thin people had some degree of manic-depressive or bipolar behavior, compared to only 3-5% of obese people. He stated: "Most people who are very thin have a short fuse. They're very irritable. They have no reserves. They're usually type A people, hyperactive. Think about that. That's because you have no fat. All that information is not being buffered. It goes to the brain."

Inadequate minerals during detoxification in underweight people: When the body is detoxifying and the person has no excess fat, the toxic fluid being released has insufficient minerals to bind with, and it poisons the surrounding tissues and active cells. Aajonus said: "If your body doesn't have nutrients all over and you're not overweight, you're going to have problems." He was happy to look at his seminar audiences and note when there were no truly skinny people present: "So, there's no skinny person here, which I'm happy to see."

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Being underweight in Aajonus's framework fits primarily into the Terrain Theory and Cooked Food / Toxicity of his causal sequence, with strong overlap into the Root Cause, Detoxification, and How to Live.

• Terrain Theory: The body's internal terrain is compromised when there is insufficient protective fat. Toxins that would otherwise be stored harmlessly in adipose tissue penetrate active cells and cause mutation and disease. The terrain of an underweight person is perpetually vulnerable.

• Cooked Food: Cooking destroys the small-molecule integrity of fat, causing fat molecules to swell 10 to 50 times their normal size. This means cooked-food eaters who think they are eating fat are consuming a biologically inaccessible form of it, one that cannot be efficiently deposited as protective cellular and tissue fat. This contributes to the underweight condition at the cellular level even in people who appear to be eating plenty of fat.

• Root Cause: The foundational cause of underweight is dietary, specifically, the absence of raw animal fat and raw animal protein in the diet, compounded by vegetarianism, excessive exercise, chronic disease, and environmental toxicity without protective fat reserves.

• Detoxification: Underweight people face the most dangerous detoxification crises because they have no fat buffer. When detox occurs, the released poisons have no fatty tissue to enter and instead damage active cells. This is why underweight people must be brought to a state of adequate fat coverage before serious detoxification work can safely proceed.

• How to Live: Aajonus's prescription that everyone, particularly those with illness, toxicity, or a history of underweight, should deliberately become 15-30 pounds (men) or 12-15 pounds (women) above their normal healthy weight fits squarely in the "How to Live" framework of protective lifestyle choices.

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Aajonus reinterpreted every major symptom associated with underweight through the lens of fat deficiency and nervous system vulnerability.

Irritability and short temper: Conventionally seen as a personality trait or stress response, Aajonus reframed this as the direct neurological consequence of insufficient fat around the nervous system. Without fat insulation, every stimulus hits the raw nerve. He said: "Most people who are very thin have a short fuse. They're very irritable. They have no reserves. They're usually type A people, hyperactive." He connected this directly to fat deficiency and said it was not a psychological but a physiological phenomenon.

Hyperactivity and never being satisfied: Aajonus consistently described thin people as perpetually restless, never content, always seeking change. He said: "Most of the thin people I know, whether they're men or women, that are thin are never satisfied. They're like Donald Trump." He attributed this not to personality but to the biochemical state of a nervous system with no fatty buffer, every metabolic signal comes through amplified and distorted.

Manic-depressive and bipolar behavior: He stated that approximately 90% of thin people exhibit manic-depressive or bipolar behavior, and that they frequently don't recognize it in themselves. He cited Arnold Ehret (the fasting and mucusless diet proponent) and Hitler (who went through thin phases) as examples of the psychological volatility associated with inadequate fat reserves. He said this contrasts sharply with obese people, of whom only 3-5% exhibit these patterns.

Physical violence and aggression: Aajonus stated that very thin people, particularly women, can be more physically violent than men in some circumstances due to the unbuffered nervous system. He cited a personal experience of a very thin woman who attacked him and broke his skin.

Weakness and inability to build strength: An underweight person, particularly one depleted of raw fat, simply cannot generate or sustain physical strength. He referenced Arnold Schwarzenegger repeatedly: when Schwarzenegger had his full fat on his body, he could lift 470-478 pounds; when he cut his fat for exhibition, he dropped to 270-275 pounds, a loss of 200 pounds of lifting capacity. "That's 200 pounds less than he could lift with the fat on. And all that muscle had no fuel, no energy, because there's no fat in the muscle." An underweight person has no muscular fuel at all.

Chronic fatigue: Aajonus described multiple patients who were profoundly underweight and suffered from chronic fatigue. Without fat to provide two-and-a-half times more energy than protein or carbohydrate can supply, the body has nothing to run on. He described a woman with 14 years of chronic fatigue who "couldn't move, couldn't do anything."

Rapid aging and deterioration: Thin people who exercise and maintain low body fat "dry out inside" and often develop aneurysms, heart and brain aneurysms, and "drop dead in their 50s." He said these are people who were considered very athletic and healthy. They are prematurely aged because they lack the fat that lubricates every cell and tissue.

Looking old from being skinny: Aajonus described Jeff Slay at 29-30 years old looking like "an Auschwitz victim who was 68 years old, literally looked that old being that skinny."

Susceptibility to illness during detoxification: When an underweight person detoxifies, released toxins have no fat to enter and instead cause cellular damage, headaches, bloating, and intense symptoms. He said: "If you detoxify and you don't have a lot of fat in your body, you will feel it. Because your body will start ripping fats out of your cells. They will suffer. They'll get hungry. They'll get bloated. They have headaches."

Dryness and brittleness: He described athletes and thin people who exercise excessively as becoming "brittle inside", dried out at the cellular level. This manifests as internal fragility even when external musculature appears developed.

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Aajonus gave extraordinarily detailed and specific food protocols for underweight individuals, built around the systematic rebuilding of fat reserves using raw animal fats and raw animal proteins.

The fundamental principle: Get fat. Eat fat. Become fat. He said repeatedly: "You need to eat a lot of fats and you need to be fat if you want to get well fast." He said this to people who appeared already thin or sick. He stated: "If you have a problem, get fat. If you want to get well in your week, get fat."

Target weight gain, men: Aajonus recommended that men gain 15 to 30 pounds above their normal healthy weight (not above a thin baseline, but above a genuinely healthy normal weight). He said: "That doesn't mean a thin weight. That means when you get to a good normal sized weight then you gain 15-30 pounds above that."

Target weight gain, women: For women, he said 12-15 pounds above normal healthy weight, though he mentioned compromising to this figure from a preferred 15-25 pounds. In the Recipe book he specified 12-15 pounds for women. He said: "I suggest people get 15 to 30 pounds overweight, but I've compromised 12 to 15 pounds overweight, which your normal weight should be." For sick women in particular, he said: "Sick women should be at least 15 pounds overweight. I prefer 25 if you want to get well fast."

Timeline for achieving the target weight: He stated the excess weight should be achieved within two months and maintained for another two months. That four-month cycle allows the body to utilize the stored fats as solvents to withdraw toxins from deep tissue.

Two wardrobes: He recommended literally acquiring two sets of clothes, one for the trim size, one for the oversized phase. He said: "Women should gain at least two sizes larger than their trim size. Men and women, get a temporary belly; it is healthier on and off!" He personally described wearing 33-34 inch waist pants as his "fat clothes" when his normal was 31 inches.

Raw butter: Aajonus described consuming at least two pounds of raw unsalted butter weekly. This was a cornerstone of fat-building. He said raw butter molecules are tiny and deposit throughout the tissues efficiently.

Raw cream: He recommended a quart of raw heavy cream weekly (heavy, thick cream). In earlier phases of his own recovery, he drank a quart of raw cream daily along with carrot juice and raw eggs.

Raw eggs: He described consuming raw eggs regularly as a core fat and protein source. During his own rebuilding phase, he was consuming raw eggs blended into his quart of carrot juice and quart of cream daily. He described Austrian athletes eating raw eggs daily as their standard protocol.

Raw meat: For bodybuilding or significant weight gain in underweight patients, he specified: "Just eat a pound of meat twice daily with a whole lubrication formula." The lubrication formula consists of egg, butter, lemon juice, and a tiny bit of honey. This formula is consumed with the meat meal so the body can burn the fat rather than the protein, allowing the protein to go toward building tissue. He stated that one patient who was 6 feet and 130 pounds (extremely thin), after putting on about 20 pounds on the diet over two years, was then given this protocol: a pound of meat twice daily with the lubrication formula. After two and a half to three and a half months on this protocol, the patient put on four inches on his arms and six inches on his chest.

The lubrication formula (for building muscle while underweight): - Raw egg - Raw butter - Lemon juice - A tiny bit of honey - Consumed with each meat meal to provide fat fuel so the protein can be used for tissue building rather than burned as energy

Raw dairy: Raw milk and raw cheese in addition to cream and butter. He mentioned raw cheese as an important part of his own early recovery. No-salt-added raw cheeses were mentioned in the weight gain context.

Carrot juice with cream for underweight/depleted people: He described a specific formula for people who are detoxifying and need minerals along with protective fat: add 4 tablespoons of raw cream or 2 tablespoons of unsalted raw butter to 1 cup of carrot juice. This provides minerals to bind with the toxic fluids being released during detox while simultaneously providing fat protection.

Force-feeding: Aajonus used the word "force-feed" explicitly. He said: "On the balanced Primal Diet, 95% of us have to force-feed ourselves to become obese." He stated in his newsletter: "Fat binds with and neutralizes toxins, therefore I ask people to force-feed themselves to gain excessive fat levels to harness and bind with toxins that are stored in their bodies. Excessive fat allows our bodies to cleanse faster, safer and more thoroughly with less symptoms. Resultantly, we heal faster, safer and more thoroughly." This is not optional gentle encouragement, it is a deliberate protocol of eating beyond hunger signals.

Meat frequency for very thin people, the cycling protocol: Aajonus described a specific cycling protocol for very thin individuals: two days of eggs, one day of meat, two days of eggs, one day of meat. He contrasted this with the protocol for very overweight people (three days meat, one day egg, three days meat). He said: "If somebody is very thin, I will tell them to do the opposite. Two days egg, one day meat, two days egg, one day meat." This cycling was to be done for six to eight weeks or however long needed.

Warning about shaking: He told very thin people not to wait until they are hungry in the stomach to eat. If they start shaking, that means they are "dangerously low in protein", dangerously low meaning that if they stand up too quickly, they could pass out and hurt themselves. He said: "For some people, I will tell them to have two days of meat in a row. One day of juice, two days of meat. I mean one day of egg, two days meat, one day of egg."

Raw animal fat specifically (not plant fat): He was explicit that the fat must be raw and animal-derived. Plant fats have larger molecules that herbivores can process but humans cannot efficiently break down to the small size needed. He said: "It takes an herbivore to digest and break it down to a smaller molecule." Coconut is the closest plant-based equivalent, at 80% fat, 15% protein, 5% carbohydrate, but even coconut fat is not comparable to raw animal fat in bioavailability.

Avocados, fresh coconut cream, raw cheese, raw cream: He listed these as the fat sources within the high-fat raw diet: "unsalted butter, no-salt-added cheeses, cream, avocados, fresh coconut cream, eggs and meat." He stated only about 28% of those on this high-fat raw diet gain more than an inch or three and retain it for a while.

Body fat percentage targets: - Women: approximately 30% body fat - Men: approximately 30% body fat (he said "men, 30 percent" as a healthy target) - Athletes who maintain 7-8% body fat will "dry out" and cannot train beyond 30 minutes without becoming brittle internally

For cancer patients who are underweight: He was even more emphatic, saying all his cancer clients must get excessively overweight. He explained: "The reason I say that all my cancer clients have to get excessively overweight is for that protection, because once the cells start dissolving, the dead cells start...", implying the need for fat to capture and contain the debris and toxins from dissolving cancerous tissue.

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Recovery from underweight on the Primal Diet is described by Aajonus as a long, nonlinear process involving deliberate fat accumulation, tissue rebuilding, cycling between weight gain and weight loss, and, for the most severely depleted individuals, potentially years or even a decade or more before complete restoration.

The initial phase, deliberate fat accumulation: For most people starting from an underweight state, Aajonus wanted them to gain their target excess weight (15-30 pounds for men, 12-15 pounds for women, more for seriously ill patients) within the first two months on the diet, and then maintain that excess weight for at least another two months. This four-month minimum cycle was the foundation.

Cycling, gaining and losing: He specifically recommended that men go through cycles of gaining the extra 15-30 pounds and then losing it, then gaining it again. He said: "And that's what I suggest for men. Men, 15-30 pounds over their normal weight. That doesn't mean a thin weight. That means when you get to a good normal sized weight then you gain 15-30 pounds above that. And women, I'm very, very kind, 10-12 pounds over your normal weight. And it works. Because what happens is you put on the extra fat the body can do deep tissue cleansing." Each cycle pulls toxins from deeper tissue, like oil in a car grabbing carbons and metal shavings.

For mildly depleted people: Patients who weren't severely ill but were thin could begin gaining weight within months. He described a man in his mid-50s who had been skinny his entire life and within one to one and a half years on the diet was able to put on weight and begin building muscle, eventually gaining 20 pounds (from 130 pounds to 150-155 pounds at 6 feet) and then further building four inches on his arms and six inches on his chest in two and a half to three and a half months with the intensive bodybuilding protocol.

For seriously ill underweight patients: The timeline is much longer. The woman with chronic fatigue from age 14, breast cancer, hip cancer, and kidney/adrenal cancer, who was extremely thin at 5'5", "would never gain the weight that I wanted her to." He wanted her to gain 20-25 pounds but she only achieved 15 pounds above her previous weight and still looked thinner than most. He noted that the process of getting her energy back after starting the diet took about a year and a half.

For frightfully thin patients (the worst cases): People who were at the extreme end of underweight, like the 98-pound woman at 5'10" or Jeff Slay at 68 pounds, had to go to the opposite extreme before the body could heal. He said: "They become the fattest. I mean, I've had patients go from this skinny, skinny, you know, like 98 pounds and 5'10", as women and men, go all the way up to 260, 280 pounds. And only the ones that were frightfully skinny do that." This extreme fat accumulation was necessary because "these people have to have a tremendous amount of fat to be able to hold that fat once it leaves the cell. Or else it will cause more damage throughout the system."

For the Olympic gymnast case: A world athlete who was at 98 pounds and gained 200 pounds to reach 300 pounds, it took her seven years on the diet before she began losing the weight. Her husband was the same way, requiring six years before weight loss began. But he noted: "The longer they were eating the fats. And putting on the new fats. Their lives got better easier. They could handle the stress of the weight."

Long-term expectation, becoming "fat and slim": Women who had been on the Primal Diet 12 to 14 years, Aajonus said, eventually became "fat and slim", carrying high body fat percentages (he cited 27% on a woman who appeared as slender as any thin person in the room) but with a trim physical appearance because raw fat molecules are tiny. He described one woman with breast cancer in 1988 or 1989 who by 2008, approximately 20 years later, looked "so trim, slim" and yet weighed in at 27% body fat on the scale.

For people coming from vegetarianism (the most resistant cases): He said it "takes generations to re-educate" mutated cells back to health. A cell that has been directly damaged by toxins (because there was no fat to absorb them) is mutated, and healing requires generational cellular turnover. This is why vegetarian and formerly vegetarian patients who are underweight are the hardest to bring back to health.

How long to stay deliberately fat: Aajonus said he would "encourage everybody to be fat for at least 7 years" and ideally to remain carrying excess fat "indefinitely through the 40 years" as long as one lives in a toxic society. He said explicitly: "As long as you're in a toxic society, still don't stay too slender."

His own personal timeline: He described his own recovery from extreme illness (during which he was dangerously thin) as a multi-decade process. He noted that his waist, which was 38-39 inches at his biggest recovery phase (when he was swollen with good fat from drinking a quart of carrot juice with a quart of raw cream daily plus raw cheese and raw meat three times a week), eventually stabilized over decades. By the time of his seminars, his waist ranged from 30 to 37 inches depending on where he was in his travel-induced weight cycle. He noted: "The healthier I get the less fat my body wants to store on it but I'm still two times more than an athlete and two times more than the Masai."

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