Who the Fat Loss Sprint Is NOT For

This content is for informational purposes only and does not constitute medical or nutritional advice. Speak with your health professional before starting this protocol.

Critical disclaimer: This article lists absolute and relative contraindications to the Fat Loss Sprint protocol. Read it in full before starting. If any absolute contraindication applies to you, do not start this protocol under any circumstances. If any relative contraindication applies, do not start without first discussing it with your health professional.

Read This Before You Start

The Fat Loss Sprint is a medically serious protocol. It is safe and effective for the right candidates. For others, it carries real risks. This chapter covers who should not use the sprint, and who should speak with their health professional before considering it.

If any condition listed below applies to you, do not proceed without explicit clearance from a qualified healthcare provider. In several cases, the protocol should not be attempted at all.

Note: The Fat Loss Sprint guide in this app is for self-guidance only. It is not a supervised clinical programme and does not provide medical monitoring. If you have any of the conditions listed in this chapter, speak with your health professional before starting. This chapter exists to help you make an informed decision about your own suitability — not to replace medical advice.

Hard Eligibility Boundaries

These limits apply regardless of health status or motivation. They are fixed protocol parameters, not clinical judgments.

If you fall outside any of these parameters, do not proceed.

Absolute Contraindications

These are non-negotiable. No amount of motivation justifies proceeding when any of the following apply.

Pregnancy or Breastfeeding

Severe caloric restriction during pregnancy risks fetal growth restriction, nutrient deficiency complications, ketosis-related harm, and preterm birth. During breastfeeding, very low calorie intake can reduce milk production, alter milk composition, and mobilise fat-stored toxins into breast milk.

If you are pregnant, planning to become pregnant in the near term, or breastfeeding: do not use the Fat Loss Sprint. If you discover you are pregnant during a sprint, stop immediately and contact your obstetrician.

Type 1 Diabetes

People with Type 1 diabetes produce little to no endogenous insulin. The dramatic drop in carbohydrate and calorie intake during the sprint creates extreme difficulty in insulin dosing, high risk of severe hypoglycaemia, and elevated risk of diabetic ketoacidosis, which can be life-threatening.

Note: Type 2 diabetes is a favourable indication for the sprint. Type 1 and Type 2 are fundamentally different conditions with different metabolic profiles and risks.

Active or Unstable Cardiovascular Disease

Very low calorie protocols can alter cardiac electrophysiology, particularly prolonging the QT interval. This raises the risk of potentially fatal arrhythmias. Historical cases of sudden cardiac death during early liquid protein diets in the 1970s were attributed to this mechanism, compounded by poor protein quality and inadequate electrolyte supplementation.

Do not use the sprint if you have:

• Recent myocardial infarction (within 6 months)
• Recent stroke or TIA (within 6 months)
• Unstable angina
• Decompensated heart failure
• Uncontrolled cardiac arrhythmias
• Prolonged QT interval (QTc above 450 ms in men, above 470 ms in women)

Well-controlled, stable cardiovascular disease is a relative rather than absolute contraindication and may be manageable after clearance from your cardiologist or GP.

Active Eating Disorders

The severe restriction in the sprint protocol can trigger, worsen, or reinforce disordered eating patterns. For anyone with active anorexia nervosa, bulimia nervosa, or binge eating disorder, the protocol risks reinforcing restrictive behaviour and body image distortion, triggering binge-purge cycles, and worsening existing medical and psychological complications.

• Active anorexia nervosa: absolute contraindication
• Active bulimia nervosa: absolute contraindication
• Active binge eating disorder: absolute contraindication
• History of eating disorders currently in remission: relative contraindication (see below)

Severe Hepatic Disease

The liver manages ketogenesis, gluconeogenesis, and protein metabolism — all dramatically altered during the sprint. Active liver disease impairs these processes and raises the risk of metabolic decompensation.

Do not use the sprint with:

• Cirrhosis (any stage)
• Active hepatitis (viral, autoimmune, or alcohol-related)
• Liver failure or significantly impaired liver function
• Hepatic encephalopathy

Note: Non-alcoholic fatty liver disease (NAFLD) without cirrhosis or significant fibrosis is generally improved by the sprint protocol and is not a contraindication.

Severe Renal Disease

High protein intake increases the kidneys' metabolic workload. In people with significantly impaired kidney function, this can accelerate renal decline. Electrolyte shifts from severe caloric restriction are also more dangerous when renal regulation is compromised.

Do not use the sprint with:

• Chronic kidney disease Stage 4 or 5 (eGFR below 30 mL/min)
• Dialysis
• Recent acute kidney injury

Mild to moderate CKD (Stages 1–3) may be manageable with modified protein targets and close monitoring, but requires nephrology consultation.

Active Cancer or Cancer Treatment

Active cancer and cancer treatment create significant metabolic stress. Severe caloric restriction during chemotherapy, radiation, or immunotherapy can compromise immune function, impair treatment efficacy, and accelerate muscle wasting. The nutritional priorities during cancer treatment are fundamentally different from those during elective fat loss.

Cancer survivors in remission who are cleared by their oncologist may be appropriate candidates, depending on their specific situation.

Under 18 Years Old

Children and adolescents have nutritional requirements related to growth and development that are incompatible with standard sprint-level restriction. Nutrient deficiencies during growth can have permanent consequences for bone density, brain development, and pubertal maturation.

Modified PSMF protocols have been studied in severely obese adolescents, but only in tertiary care paediatric obesity programmes under strict medical supervision. These are clinical interventions, not self-directed programmes.

Severe Psychiatric Disorders

Active, severe psychiatric illness can impair the ability to safely follow the protocol, make informed decisions, and recognise warning signs. Severe caloric restriction can also exacerbate certain psychiatric conditions.

This includes:

• Active psychosis or severe thought disorders
• Severe, untreated depression with suicidal ideation
• Active substance use disorders
• Severe cognitive impairment

Relative Contraindications

These conditions increase risk but do not absolutely preclude the sprint. Proceeding may be possible with modifications, enhanced monitoring, and specialist input.

Age Over 70

Sarcopenia (age-related muscle loss) is already accelerated in older adults. Severe caloric restriction further increases lean mass vulnerability. Older adults are also more susceptible to electrolyte imbalances, dehydration, and orthostatic hypotension.

If proceeding: the full FLS protein target of 2.2–3.0 g/kg lean body mass, mandatory resistance training, weekly blood work, sprint duration limited to a single Sprint Level 1 sprint only (14 days maximum), close electrolyte monitoring, and falls risk assessment.

History of Eating Disorders (Currently in Remission)

The structure and restriction of the sprint may trigger relapse, even when the person is currently stable.

Requirements if considering the sprint: clearance from a mental health professional familiar with your history, regular psychological check-ins during the sprint (at least biweekly), clear criteria for stopping if disordered patterns return, and a trusted support person who knows the protocol and can monitor your behaviour.

Gout or Hyperuricemia

Rapid weight loss raises uric acid levels due to increased purine metabolism and competition between uric acid and ketone bodies for renal excretion. This can trigger acute gout attacks.

If proceeding: discuss prophylactic uric acid-lowering therapy with your health professional, monitor uric acid every 2–4 weeks, maintain aggressive hydration (3+ litres per day), and be prepared to pause if an attack occurs.

Gallbladder Disease or History of Gallstones

Rapid weight loss is a well-established risk factor for gallstone formation. Approximately 10–25% of people undergoing rapid weight loss develop new gallstones, and roughly 2–3% develop symptoms requiring cholecystectomy.

If proceeding: gallbladder ultrasound before starting, consider ursodeoxycholic acid (ursodiol) 300 mg twice daily as prophylaxis (prescription required), include at least 10–15 g dietary fat per day to maintain gallbladder motility, and stop immediately if right upper quadrant pain, nausea, or jaundice develops.

Medications That Complicate Management

Stable Cardiovascular Disease

Electrolyte shifts, potential dehydration, and QT changes create manageable but real risks even in well-controlled cardiac conditions.

Requirements: ECG at baseline and every 4 weeks, electrolyte monitoring every 1–2 weeks, cardiology clearance, blood pressure monitoring at least twice weekly, and immediate discontinuation if palpitations, chest pain, or syncope occur.

Thyroid Disorders

The sprint naturally reduces T3 (active thyroid hormone) as part of metabolic adaptation. This compounds issues in pre-existing hypothyroidism. Hyperthyroidism creates excess metabolic demand incompatible with severe restriction.

Stable, well-controlled hypothyroidism on levothyroxine is generally acceptable with TSH monitoring every 4 weeks. Newly diagnosed or poorly controlled thyroid conditions should be treated and stabilised before beginning.

BMI Below 27 Without Comorbidities

Lower body fat means less metabolic reserve and a higher proportion of lean mass loss during restriction. The risks of the sprint increasingly outweigh the benefits as starting BMI falls below 27.

• BMI 25–27 without comorbidities: consider a moderate caloric deficit instead
• BMI below 25: the sprint is not appropriate — this body composition does not warrant severe restriction

Warning Signs: When to Stop

Even appropriate candidates can encounter problems. Know when to act.

Stop Immediately and Seek Medical Attention

• Chest pain, palpitations, or irregular heartbeat
• Severe dizziness, fainting, or near-fainting
• Severe abdominal pain, particularly upper right quadrant (possible gallbladder)
• Confusion or altered mental status
• Severe muscle weakness beyond normal dieting fatigue
• Dark urine or significantly reduced urine output
• Severe muscle cramps not resolving with supplementation, tingling or numbness in extremities, or irregular heartbeat

Pause and Consult Your Healthcare Provider

• Excessive or distressing hair loss
• Persistent nausea, vomiting, or inability to tolerate food
• Symptoms of depression, anxiety, or disordered eating
• Menstrual irregularity lasting more than two cycles
• Sudden joint pain suggestive of gout
• Persistent cold intolerance, extreme fatigue, or constipation not responding to supplementation
• Any new or concerning symptom that was not present before the sprint

When to Speak With Your Health Professional First

The Fat Loss Sprint is a self-guided protocol — this app is a guide, not a clinical supervisor, and it does not provide medical monitoring or oversight. For certain conditions and circumstances, consulting your own health professional before starting is essential. Specifically, speak with your health professional before starting if:

1. You have any of the relative contraindications listed in this chapter
2. You take medications that may need adjustment during the protocol (particularly insulin, sulfonylureas, antihypertensives, or lithium)
3. You have any cardiovascular, renal, hepatic, or psychiatric condition not listed as an absolute contraindication
4. You are unsure whether any condition you have affects your suitability
5. You are over 70 or have a history of eating disorders

The steps your health professional may recommend — baseline screening, medication review, and a transition plan for after the sprint — are your responsibility to arrange with your own healthcare provider. This app cannot perform or replace that process.

References

1. National Heart, Lung, and Blood Institute. (1998). Clinical guidelines on the identification, evaluation, and treatment of overweight and obesity in adults. NIH Publication No. 98-4083. Available at: NCBI Bookshelf

2. Caprio, M., Infante, M., Moriconi, E., et al. (2019). Very-low-calorie ketogenic diet (VLCKD) in the management of metabolic diseases: systematic review and consensus statement from the Italian Society of Endocrinology. Journal of Endocrinological Investigation, 42(11), 1365–1386. DOI: 10.1007/s40618-019-01061-2

3. Muscogiuri, G., El Ghoch, M., Colao, A., et al. (2021). European guidelines for obesity management in adults with a very low-calorie ketogenic diet: a systematic review and meta-analysis. Obesity Facts, 14(2), 222–245. DOI: 10.1159/000515381

4. Atkinson, R. L. (1989). Low and very low calorie diets. Medical Clinics of North America, 73(1), 203–215. DOI: 10.1016/S0025-7125(16)30700-X

5. Sours, H. E., Frattali, V. P., Brand, C. D., et al. (1981). Sudden death associated with very low calorie weight reduction regimens. American Journal of Clinical Nutrition, 34(4), 453–461. DOI: 10.1093/ajcn/34.4.453

6. Festi, D., Colecchia, A., Orsini, M., et al. (1998). Gallbladder motility and gallstone formation in obese patients following very low calorie diets. International Journal of Obesity, 22(6), 592–600. DOI: 10.1038/sj.ijo.0800631

7. NICE. (2014). Obesity: identification, assessment and management. Clinical guideline [CG189]. Available at: nice.org.uk

8. American Dietetic Association. (1990). Position of the American Dietetic Association: very-low-calorie weight loss diets. Journal of the American Dietetic Association, 90(5), 722–726. PMID: 2186078

9. Paoli, A., Cerullo, G., Bosco, G., et al. (2020). Scientific evidence underlying contraindications to the ketogenic diet: an update. Obesity Reviews, 21(10), e13053. DOI: 10.1111/obr.13053