The continuum of the degree of carbohydrate restriction that exists in contemporary clinical
practice is illustrated in Table 1 [23], with general agreement that less than 20 g per day is a “very low”
carbohydrate intake (though some use a threshold of less than 50 g), equivalent to about 10% of total
energy intake. The threshold for “low” carbohydrate intake is usually accepted as less than 130 g/day,
equivalent to less than 26% of total energy from carbohydrates. Consumption greater than 230 g per
day is consistent with no restriction of carbohydrate, although we find that many of our patients with
diabetes or obesity exceed several times this amount on a daily basis. In general, the greater the degree
of carbohydrate restriction, the greater the degree of ketogenesis, such that carbohydrate intakes of
more than 50 g per day are not usually sufficient for ketogenesis [10]. Hence, “low-carbohydrate” and
“ketogenic” are not synonymous dietary terms, but do overlap.

8.1. Guidelines Endorse Low-Carbohydrate and VLCKD Diets.
Doctors, nurses and other health care professionals ought to be aware that the use of
low-carbohydrate and VLCKD diets in patients with obesity or type 2 diabetes is in fact supported by
several sets of guidelines from international bodies and professional groups, as outlined in Table 2.
For example, the most recent guidance from the American Diabetes Association is unequivocal in
stating that “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”. [86]. In the UK, pragmatic infographic resources based on
the glycaemic load of various foods are available from the National Institute for Health and Care
Excellence (NICE) (created by one of the authors (D.U.) [92]. See Figure 2 for an example. These help
patients understand the glycemic “consequences” of their dietary choices. For example, a 150 g bowl of
boiled rice has approximately an equivalent impact on blood glucose levels as ten standard teaspoons
of table sugar.

For example, the most recent guidance from the American Diabetes Association is unequivocal in
stating that “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.” [86]. 

8.2. Early De-Prescription is Important
Although research data are relatively scarce on optimal patterns of medication usage early in
low-carbohydrate and ketogenic diets, we have found that early and intensive de-prescribing is often
required, particularly in patients with diabetes [93]. In particular, rapid titration of insulin is
obviously important in order to prevent potentially serious hypoglycemia. (This clearly applies only
to patients with an established diagnosis of insulin requiring type 2 diabetes, as opposed to type 1
diabetes: Low-carbohydrate diets have been shown to reduce adverse events and improve control in
observational studies in patients with type 1 diabetes [94], but we have not considered this further
here.) In general, we tend to stop all fast-acting insulin at the time of initiation of VLCKD and, if not
stopping basal insulin completely, by then reducing the dose by between 50% and 80%. This
mandates four-times-daily monitoring of capillary blood glucose levels in the hours and days after
significant decreases in carbohydrate intake. We have found that it is essential that these patients
have immediate access to a diabetes nurse, primary care doctor, consultant or dietitian with
experience of low-carbohydrate diets during this time. In addition, we tend to stop sulphonylurea
drugs completely at initiation of the diet because of the risk of hypoglycemia. Conversely, we tend to
continue metformin given its insulin-sensitizing effects, cardiovascular benefits. and very low risk of
hypoglycemia. We take an individualized approach to titrating gliptins or glitazones, informed by
baseline HbA1c and patient preference. We often continue glucagon-like peptide-1 (GLP1) receptor
agonists. Given the potential risk of euglycemic diabetic ketoacidosis [95] in patients taking sodiumglucose cotransporter-2 (SGLT2) inhibitor drugs, we always stop these if the diet is initiated.

8.3. Calorie Counting Is Not Required
Rather than emphasizing the need for patients to quantify their calorie intake, we ask them to
focus on eating to comfortable satiation and then stopping. The effectiveness of calorie counting
has been questioned [97,98] with well-described physiological “recidivism” with this approach [99].
We take a more mechanistically intuitive approach, emphasizing to the patient that metabolic changes
associated with their reduced carbohydrate intake may adjust their “hunger set-point” as outlined
above. We often try to back this engagement and education up with graphical aids, emphasizing
the physiological mechanisms underlying insulin resistance and their reversal with carbohydrate
restriction, as shown in Figure 3. Our anecdotal experience of patients reporting significantly reduced
hunger and increased satiety is consistent with studies on higher fat and protein diet influence on the
physiological drivers of feeding behavior [100,101].
The second group of drugs that need consideration during a low-carbohydrate diet is
antihypertensive medications. This is because the higher circulating insulin levels in insulin resistant
type 2 diabetes patients can cause renal sodium retention, which may be reversed quickly with a
reduction in insulin levels (as part of a low-carbohydrate diet), leading to enhanced renal sodium
(and water) excretion and a lower blood pressure [96]. We (D.U.) have described these changes in a
cohort of 128 patients with type 2 diabetes on a low-carbohydrate diet for an average of two years
[75], where there was a reduction in systolic and diastolic blood pressure of 10.9 and 6.3 mmHg,
respectively, despite a 20% reduction in anti-hypertensive medication usage. The risk of hypotension
mandates cautious and frequent monitoring of patients’ blood pressure and vigilance for symptoms
of postural hypotension.

8.4. Monitor Cardiovascular Risk Factors
While all patients with obesity and type 2 diabetes should have cardiovascular risk factors
monitored periodically, the potential increase in fat consumption that arises on a low-carbohydrate diet,
in the context of historical epidemiological concerns that dietary fat might increase cardiovascular risk,
makes the issue more pertinent. We have found that individuals concerned about the appropriateness
of low-carbohydrate diets are either unfamiliar or don’t accept recent nutritional epidemiological
discoveries around the ineffectiveness of low fat diets to prevent cardiovascular disease [29] and the
benefits of low-carbohydrate intake [102] and certain saturated fats, such as those from dairy, in reducing
cardiovascular (and diabetes) risk [103,104]. A recent meta-analysis suggested low-carbohydrate
diets are superior to low fat diets in improving the lipid profile [105]. While current guidelines on
saturated fat are overdue a revision [106,107], it seems reasonable to reassure patients undertaking
a low-carbohydrate diet, and their health care providers, that saturated fats from foods that are not
ultra-processed are unlikely to do them harm, especially if they are losing weight and improving
glycaemia while undertaking a low-carbohydrate approach. A second consideration is the increase
in LDL-cholesterol that is described with some [27] but not all [108] low-carbohydrate interventions,
but the fact that this appears limited to the large LDL subfraction [76] suggests it is unclear whether it
increases cardiovascular risk. Nonetheless, we routinely measure blood pressure, lipid profile and
HbA1c in patients adhering to a low-carbohydrate or VLCKD and treat abnormal findings as we would
in routine clinical practice, where they have not improved over time.

8.5. Ensure Adequate Fiber Intake
While the recommended intake of dietary fiber is 30 g per day (in the UK) the average intake is
closer to 18 g per day. The reduction in wholegrain consumption associated with a low-carbohydrate
diet could accentuate that deficit and low intake of dietary fiber is associated with an increased risk
of metabolic [109] and colonic [110] disease. However, we have found in practice that adopting
a low-carbohydrate diet which limits ultra-processed foods and includes nuts, seeds, non-starchy
vegetables and low-carbohydrate fruits tends to lead to a net gain rather than a reduction in patients’
dietary fiber intake compared to baseline.

Table 2. Summary of current guidelines and consensus statements on the use of low-carbohydrate diets.

This entry is adapted from the peer-reviewed paper 10.3390/ijerph17072557