Basic Nutrition Overview

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

Note: The nutritional principles described here are general educational content. Individual requirements vary significantly based on body composition, health status, and activity level. Do not apply these as personal targets without completing your own sprint setup calculation.

Why Nutrition Fundamentals Matter Here

The Fat Loss Sprint is defined by its macronutrient targets, not just its calorie level. To follow the protocol correctly, you need to understand what each macronutrient does, why each target is set where it is, and how the numbers interact. This chapter gives you that foundation.

Calories: The Starting Point

A kilocalorie (what nutrition labels call a "calorie") is the energy required to raise one kilogram of water by one degree Celsius. Your body burns calories to run every process: temperature regulation, organ function, nerve signaling, muscle contraction, digestion (Atwater & Woods, 1896).

When you eat more than you burn, the surplus is stored, mostly as body fat. When you burn more than you eat, the deficit is covered by mobilizing stored fuel, primarily from adipose tissue, and when protein is inadequate, from lean tissue too. This is well established: it is how every diet produces fat loss, regardless of macronutrient composition (Hall et al., 2012).

What is more nuanced: both sides of the energy equation are dynamic. Your metabolism adjusts in response to restriction. The composition of your diet affects how your body partitions energy between fat storage and lean tissue. These details are why the Fat Loss Sprint specifies precise macronutrient targets rather than just a calorie number.

Where Your Calories Go Each Day

Your total daily energy expenditure (TDEE) has four components (Levine, 2005):

NEAT is the most variable component between individuals and the one most suppressed during caloric restriction. This is relevant to how your sprint affects your metabolism, covered in "Nutrient Metabolism During a Sprint".

Protein: The Foundation

What Protein Does

Protein builds and repairs muscle, drives enzymatic reactions, produces hormones (including insulin and growth hormone), carries oxygen (hemoglobin), fights infection (antibodies), and, when needed, provides energy at 4 kcal per gram.

There are 20 amino acids. Nine are essential: your body cannot make them, so they must come from your diet. Those nine are histidine, isoleucine, leucine, lysine, methionine, phenylalanine, threonine, tryptophan, and valine (Institute of Medicine, 2005).

Protein Quality

Not all protein sources are equal. Quality depends on two things: amino acid profile (does it contain all essential amino acids?) and digestibility (how efficiently can your body use them?).

High biological value sources contain all essential amino acids in proportions closely matching human requirements:

• Eggs (the reference protein, biological value of 100)
• Whey protein (biological value ~104)
• Lean meat, poultry, and fish
• Dairy

During a Fat Loss Sprint, protein quality matters more than usual. With calories severely restricted, every gram of protein needs to contribute maximally to preserving your lean mass. The protocol emphasizes whole food high-quality protein sources for this reason (Bistrian, 1978).

Muscle Protein Synthesis

Your muscle tissue is in constant turnover: simultaneously breaking down (muscle protein breakdown, MPB) and rebuilding (muscle protein synthesis, MPS). Net lean mass is the balance between those two processes (Phillips & Van Loon, 2011).

Protein intake stimulates MPS in a dose-dependent way, up to roughly 20–40 g of high-quality protein per meal depending on your age and lean body mass. Leucine is the key trigger, with a threshold of approximately 2.5–3 g of leucine per meal required to maximally stimulate MPS (Morton et al., 2015; Churchward-Venne et al., 2012).

During caloric restriction, MPB tends to increase and the MPS response to protein can be blunted. Higher-than-normal protein intake counteracts this tendency (Phillips et al., 2016).

Your Protein Targets

Standard protein recommendations for healthy adults in energy balance are 0.8 g/kg per day. That number is designed to prevent deficiency, not to protect lean mass during severe restriction.

During a Fat Loss Sprint, your targets are significantly higher:

Four reasons protein requirements are higher during your sprint:

1. Gluconeogenesis demand: With carbohydrates severely restricted, your body synthesizes glucose from amino acids. Adequate dietary protein means your muscle protein doesn't have to be the source (Cahill, 2006).
2. Nitrogen balance: Higher protein intake maintains positive nitrogen balance, the metabolic marker of lean mass preservation (Bistrian et al., 1976).
3. Satiety: Protein is the most satiating macronutrient per calorie. On a protocol where food volume drops dramatically, this matters (Leidy et al., 2015).
4. Thermic effect: 20–30% of protein calories are expended in digestion and metabolism, effectively increasing your deficit at no extra hunger cost (Calcagno et al., 2019).

Fat: Essential Minimum Only

What Fat Does

At 9 kcal per gram, fat is the most calorie-dense macronutrient. It forms cell membranes, produces steroid hormones (testosterone, estrogen, cortisol), transports fat-soluble vitamins (A, D, E, K), and regulates inflammation through omega-3 and omega-6 fatty acid pathways (Calder, 2015).

Two fatty acids are essential: linoleic acid (omega-6) and alpha-linolenic acid (omega-3). Your body cannot synthesize them. Adequate intake for adults is approximately 11–17 g/day of linoleic acid and 1.1–1.6 g/day of alpha-linolenic acid (Institute of Medicine, 2005).

Fat During Your Sprint

Fat intake is the most restricted macronutrient during a sprint. The reasoning is direct: when your goal is to maximize oxidation of stored body fat, providing large amounts of dietary fat reduces your reliance on endogenous fat stores. You want your body pulling from adipose tissue, not from what you just ate.

That said, fat intake must not drop to zero. Fat intake is fixed by your Sprint Level: 30 g/day (Level 1), 27 g/day (Level 2), or 25 g/day (Level 3). This meets essential fatty acid requirements and supports fat-soluble vitamin absorption when combined with fish oil supplementation. The fat in your protocol comes from two sources: what's naturally present in lean protein sources, and your supplemental fish oil providing EPA and DHA.

Carbohydrates: Strategic Restriction

What Carbohydrates Do

Carbohydrates provide 4 kcal per gram and are the body's preferred fuel for high-intensity activity. Under normal dietary conditions, the brain uses approximately 120 g of glucose per day. Liver glycogen (~80–120 g) buffers blood glucose between meals. Muscle glycogen (~300–500 g, depending on muscle mass and training status) fuels muscular contraction.

Carbohydrate intake is also the primary stimulus for insulin secretion. Insulin promotes glucose uptake, glycogen storage, and fat storage, while suppressing lipolysis (the breakdown of stored body fat) (Dimitriadis et al., 2011).

Why Carbohydrates Are Restricted During a Sprint

Your sprint carbohydrates come entirely from non-starchy vegetables, eaten freely. You count net carbs only — total carbs minus fibre. The target is 50 g net per day. Because cruciferous and leafy vegetables are mostly fibre, generous portions still land inside that range, and the app's carb tile gives you practical headroom up to 70 g before flagging over for the day. Two reasons this structure works:

First, insulin suppression. Low carbohydrate intake means low insulin. Low insulin removes the primary brake on lipolysis, allowing stored fatty acids to be mobilized at their maximum rate.

Second, inducing ketosis. When carbohydrate intake falls below the threshold needed to supply all glucose-dependent tissues (roughly 50–100 g/day depending on activity), the liver increases ketone body production from fatty acids. Ketone bodies (primarily beta-hydroxybutyrate and acetoacetate) serve as alternative fuel for the brain, reducing its glucose requirement from ~120 g to ~40 g per day. This reduces the demand for gluconeogenesis from amino acids, which directly protects your lean mass (Cahill, 2006).

Carbohydrate restriction is temporary and strategic. During planned refeeds, carbohydrate intake is deliberately increased to restore glycogen, stimulate leptin production, and support thyroid hormone conversion.

Fibre: Don't Overlook It

Dietary fibre is plant-based carbohydrate that resists digestion. It provides roughly 1.5–2 kcal per gram through colonic fermentation, far less than digestible carbohydrate.

During your sprint, fibre matters for four reasons:

1. It increases meal volume and slows gastric emptying, contributing to fullness when total food intake is low
2. It supports gut health and a healthy microbiome, which can be disrupted by severe caloric restriction
3. It prevents constipation, a common issue with low food volume and low carbohydrate intake
4. Soluble fibre moderates blood glucose response during the transition to a fat-adapted state

Target a minimum of 15–25 g of fibre per day from non-starchy vegetables. If you fall short, psyllium husk supplementation fills the gap.

Caloric Density: Why Macros Matter More Than Calories on a Sprint

Fat provides more than twice the calories per gram compared to protein or carbohydrate. A sprint that restricts fat and carbohydrate while keeping protein high can achieve very low total calories while still providing substantial physical food volume. Lean protein and vegetables are bulky. This is a practical advantage for adherence.

The Thermic Effect of Food: A Built-In Advantage

The thermic effect of food (TEF) is the energy your body burns digesting, absorbing, and metabolizing what you eat. It varies dramatically by macronutrient (Calcagno et al., 2019):

Why is protein TEF so high? Because metabolizing protein is biochemically expensive: removing amino groups, synthesizing urea for excretion, running gluconeogenesis, and assembling new proteins all consume ATP (Westerterp, 2004).

In practice: if you consume 800 kcal during a sprint and 65% (520 kcal) comes from protein, approximately 104–156 kcal of that is expended through TEF alone. Your net caloric availability is closer to 650–700 kcal, widening your deficit without additional restriction.

A 2024 systematic review and meta-analysis of 52 studies confirmed that higher protein meals consistently produce greater diet-induced thermogenesis compared to lower protein meals (standardized mean difference: 0.45; 95% CI: 0.26–0.65; P < 0.001) (Rietman et al., 2024).

How the Macros Stack Up: Sprint vs Standard Diet

Standard maintenance (~2,000 kcal/day):

• Protein: 15–25% of calories (75–125 g)
• Carbohydrate: 45–55% of calories (225–275 g)
• Fat: 25–35% of calories (56–78 g)

Fat Loss Sprint (~800–1,100 kcal/day):

• Protein: 55–70% of calories (120–160 g) — set first, from lean body mass
• Carbohydrate: from non-starchy vegetables — 50 g net carbs target (fibre not counted); app allows up to ~70 g before flagging over to leave room for generous veg portions
• Fat: 20–30% of calories — fixed by Sprint Level (Level 1: 30 g/day, Level 2: 27 g/day, Level 3: 25 g/day)

The FLS never drops below 800 kcal. Total calories are not set directly — they are an output of your macro targets. Protein is calculated first from your lean body mass. Fat is fixed by your Sprint Level. Carbohydrates come from vegetables. The calorie total follows from those decisions.

The proportion of protein increases dramatically compared to a standard diet, even though the absolute amount may not change as much as you'd expect. The shift happens because total calories drop so steeply. A typical 140 g protein intake represents ~28% of a 2,000 kcal maintenance diet. The same 140 g represents ~70% of an 800 kcal sprint day.

Crucially, the sprint protocol works backward from your protein needs. Protein is set first, based on your lean body mass. A fixed fat allowance is added. Carbohydrates come from non-starchy vegetables, counted as net carbs only — 50 g per day target, with the app allowing up to ~70 g before flagging over so veg-heavy days stay in range. Total calories are the output of those decisions, not the starting point. This is fundamentally different from standard dieting, where a calorie target is set first and macros are divided as proportions.

Summary

• Calories determine the direction of weight change. Macronutrients determine the composition of that change.
• Protein is the foundation. The FLS protocol sets your target based on lean body mass, not total calories, and recommends distributing it across every meal.
• Fat is minimized but not eliminated. You need essential fatty acids for cell membrane integrity, hormone synthesis, and vitamin absorption.
• Carbohydrates are restricted strategically to promote lipolysis and ketosis, then periodically reintroduced through refeeds.
• Fibre needs active management through vegetables and supplementation.
• The high thermic effect of protein provides a hidden caloric advantage that widens your deficit without adding hunger.

References

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• Bistrian, B. R., Blackburn, G. L., Flatt, J. P., Sizer, J., Scrimshaw, N. S., & Sherman, M. (1976). Nitrogen metabolism and insulin requirements in obese diabetic adults on a protein-sparing modified fast. Diabetes, 25(6), 494–504. https://doi.org/10.2337/diab.25.6.494
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