Study Details
Table of Contents
What this guide actually says
This document is a clinician-facing guide on using therapeutic carbohydrate reduction (TCR) for people with type 1 diabetes (T1D). It compiles evidence, cautions, and practical steps for safely adopting low‑carb (50–129 g/day) or very low‑carb (20–50 g/day) eating patterns to improve glucose control and reduce the burden of insulin dosing.
- The central idea: carbohydrate drives post‑meal blood glucose the most; lowering carbs reduces glucose swings and the size and frequency of insulin doses, which can make diabetes management simpler and safer.
- TCR is presented as a valid nutrition therapy option for T1D, with acknowledgement by major organizations that low‑carb can fit individual preferences and improve glycemia.
- Success depends on close collaboration with a prescriber to proactively adjust insulin and monitor glucose, especially during the first days and weeks.
Key findings
- Lower carbs, better control: Across large reviews, less daily carbohydrate is associated with lower A1C and reduced total insulin doses in T1D, in a dose‑response manner. One meta‑regression covering 101 studies and 45,972 people found A1C and insulin needs improve progressively as carbs fall from typical intakes toward TCR. The authors quantify that every 50 g/day carb reduction is linked to about a 0.52% absolute A1C drop. Studies of very‑low‑carb often report A1C in the non‑diabetic range.
- Time in range and variability: Short‑term trials and observational reports show tighter CGM profiles, less variability, and lower insulin requirements on low/very‑low‑carb diets.
- Insulin goes down: Many people need substantially less insulin after adopting TCR; total daily insulin can fall by 25–75% once stabilized, with careful titration.
- Hypoglycemia risk management: The guide stresses that hypos come from excess insulin, not low‑carb per se. With appropriate insulin reduction and monitoring, low‑carb may reduce variability and the likelihood of severe hypos.
- Protein and fat matter too: While carbs drive immediate spikes, protein and fat can cause delayed rises (often 3–5 hours later). Insulin timing and type may need to change (e.g., split or extended boluses, or using Regular insulin).
- Ketones explained: Nutritional ketosis (regulated, symptom‑free) is distinct from diabetic ketoacidosis (DKA). TCR can raise ketones safely when insulin is adequate; everyone with T1D should know sick‑day rules and have a blood ketone meter.
- Safety notes: Rapid improvements in glucose can transiently worsen some complications (e.g., proliferative retinopathy) or trigger treatment‑induced neuropathy in those with very high baseline A1C; a phased approach and medical supervision are recommended.
Practical applications for everyday life with diabetes
- Start simple: Build meals around a protein source, two non‑starchy vegetables, and enough fat to meet energy needs. Keep daily carbs within your chosen plan (e.g., 20–50 g or 50–129 g).
- Stabilize the routine: Distribute carbs, protein, and fat across meals instead of “banking” them. Consistency helps safer insulin dosing.
- Adjust insulin proactively: Before changing diet, get an insulin plan from your prescriber. Expect prandial insulin to drop quickly and basal to change over weeks. Use CGM or frequent fingersticks and review data often.
- Watch delayed effects: Higher‑fat/protein meals may need split or extended boluses (or Regular insulin timing) to match later glucose rises.
- Mind electrolytes: Early low‑carb can increase sodium loss; adequate sodium, potassium, magnesium, fluids, and rest can ease “keto flu” symptoms.
- Treat lows the standard way: Use fast‑acting glucose/dextrose; then review doses with your care team.
- Special cases: If you have advanced complications, very high A1C, are pregnant, or supporting a child, a phased‑in approach with tight clinical follow‑up is advised.
Relevance beyond clinics
For people with T1D seeking steadier days, fewer dramatic highs and lows, and less mental load, the guide presents low/very‑low‑carb as a viable option—provided insulin is appropriately reduced and monitoring is increased during the transition. It frames TCR as a way to make the “system” more predictable by shrinking the biggest variable: carbohydrate.
Highlights
To simplify the process, individuals and caregivers may find it helpful to structure a basic TCR meal as follows:Choose a protein source (such as seafood, poultry, eggs, beef, pork, lamb, tofu or tempeh).Choose a couple of vegetable side dishes (such as broccoli, green salad, green beans, or cucumbers).Incorporate fats to enhance the flavour of the meal and to help meet energy requirements (such as olive oil, butter, ghee, tallow, salad dressing, sour cream, avocado, or the natural fat found in protein sources). Page 18
It's worth noting the importance of incorporating enough dietary fat in TCR to meet energy requirements. Sometimes individuals who are familiar with low-fat dietary guidelines do not add in enough fat to meet their body’s needs when following TCR. Failing to do so can lead to increased hunger, carbohydrate cravings, or unwanted weight loss, which may undermine the sustainability of this strategy. If the individual experiences undesired weight loss, increasing fat intake may be necessary Page 18
“Reducing overall carbohydrate intake for individuals with diabetes has demonstrated the most evidence for improving glycemia and may be applied in a variety of eating patterns that meet individual needs and preferences.”American Diabetes Association’s Nutrition Therapy for Adults With Diabetes and Prediabetes: A Consensus Report, 2019, p. 736 Page 19
The largest and most comprehensive systematic review of nutritional intake in T1D, which included 45,972 individuals living with T1D (54% female; 45% pediatric) across 101 studies, demonstrated that reduced carbohydrate intake is associated with better HbA1c levels and lower insulin requirements. This effect was observed in a dose-dependent manner, ranging from 225 grams of daily carbohydrate down to TCR (Koutnik et al., 2024c). Page 19
It’s important to note that rapid improvements in glucose control - which may occur from very low carb TCR dietary changes - can potentially exacerbate existing diabetes-related complications, such as proliferative diabetic retinopathy, or trigger new complications like treatment-induced neuropathy in patients with chronic hyperglycemia. Therefore, for individuals with existing proliferative diabetic retinopathy and those with a history of severe, chronic hyperglycemia and very high A1C, a phased-in approach to TCR dietary changes is advisable Page 36
AN INSULIN PLAN MUST BE IN PLACE PRIOR TO TCR IMPLEMENTATION. Not planning for appropriate adjustment in insulin type and dosage is THE MOST COMMON mistake when attempting to implement TCR in T1D. This should be done in consultation with the individual’s prescribing medical practitioner prior to dietary changes being made. Page 39
Potential “Keto Flu” Side Effects One aspect of supporting patients during TCR implementation is helping them manage potential mild side effects, commonly associated with ‘keto flu’, such as dizziness, lightheadedness, irritability, fatigue, headache, constipation, and muscle cramps. It’s particularly important to maintain electrolyte balance and hydration during the transition to TCR; this point cannot be overstated. To help your patients avoid feeling unwell, stress that their hydration and electrolyte balance are crucial, as reduced carbohydrate intake to low and very low amounts leads to increased sodium excretion by the kidneys, resulting in greater loss of water and salt through urine (Tiwari et al., 2007; DeFronzo, 1981). This is a normal physiologic response to reduced carbohydrate intake. Page 41
Individuals who transition from a processed food diet to a whole foods way of eating may also experience temporary symptoms such as diarrhea, constipation, fatigue, headache, joint pain, skin flare-ups, or flu-like symptoms. This may occur for those with high levels of inflammation and/or impaired liver function. Drinking plenty of water, getting proper rest, light exercise, and reducing stress can support the transition period. Page 42
Monitoring Ketone Levels It is important for all individuals with T1D to have a blood ketone meter and to know their normal ketone levels on TCR. Understanding these levels helps detect abnormal changes that may indicate the onset of diabetic ketoacidosis (DKA) Page 43
Monitoring and promptly adjusting insulin in the first 24 to 48 hours after an individual initiates TCR supports a safe and effective transition as changes in glycemic and insulin load occur at the first meal (Hengist et al., 2023) Page 52
TCR prandial dosing for protein and fat may consider:•Regular (short-acting) insulin via injection,•rapid-acting insulin via injection, which may need to be split into two bolus injections and/or given after the meal (e.g. postprandial bolus 1-2 hours after eating), or•rapid-acting insulin in a pump via split-bolus, dual wave, or extended bolus options, with extended bolus durations typically over 3-5 hours in duration. Page 53
Some individuals with closed-loop pump systems may experience stable blood glucose following a TCR meal without delivering a mealtime bolus, as their pump may automatically make insulin adjustments to maintain blood glucose in target range. Page 53
If insulin resistance is suspected due to high total daily insulin needs, reduce up to 50% for initial diet changes with an "All In, 100% Day 1" approach (see “Selecting a TCR Transition Strategy” earlier in this guide). The reason for this is that the insulin resistance component of the person’s physiology may rapidly normalize, leaving them with the underlying insulin deficiency alone. If no insulin resistance is suspected, reduce 25% or so. Page 53
Due to the TCR foods you will be eating, your mealtime insulin needs will change when you transition from a high-carb way of eating to a lower-carb way of eating. It is important for you to be aware of this, as rapid-acting insulin typically needs to be reduced (often significantly). Extra caution is needed to avoid the risk of hypoglycemia. Page 54
When following TCR and eating small amounts of carbohydrates, you may notice the following:•your blood glucose levels are not likely to rise high immediately after eating.•your blood glucose may, however, rise a little right after eating due to the carbohydrate and then gradually rise later on due to the effects of protein and/or fat.•If you eat a meal very high in fat, you may observe both a delayed glycemic response from the carbs or protein, plus the possibility of high blood glucose that begins to rise more than 3 hours after eating and into the ensuing hours.•Depending on the amount and type of dietary fat consumed, prolonged high blood glucose may occur unless insulin needs are met. Page 54
To help you transition to TCR, your prescribing medical practitioner will help you prepare an insulin dosing plan as a starting point. You are encouraged to use a CGM or to test more frequently using a glucometer, especially in the early days of your transition to TCR, to allow close monitoring of glycemic responses and to make adjustments as needed. Page 54
When you lower your carbohydrate intake, you may find that your blood glucose may become more ‘responsive’ to carbohydrate, meaning that even small amounts of carbohydrate will cause a blood glucose response. This can result in the need to strengthen bolus calculator carbohydrate ratios (insulin to carb ratio).• When following TCR, you may find you are more sensitive to insulin, and over time, this will result in the need to weaken correction/sensitivity bolus calculator ratios and reduce basal insulin rates.•If you experience hypoglycemia on a TCR diet, you treat it the same way you treat hypoglycemia at any other time - with a fast-acting carbohydrate, preferably using glucose or dextrose. Page 54