Health and nutrition education interventions appeared to be the ones that achieved the greatest salt reduction, with salt reduction ranging from about 0.9 g/day to 4.7 g/day. Salt reduction in nutritional education, plus other interventions, ranged from about 0.57 g/day to 4.5 g/day. Estimates of salt intake interventions reduced salt intake between about 0.4 and 2.1 g/day. However, it is important to keep in mind that the mean baseline sodium value varied widely across all interventions. Reductions in higher basal values seems to can reach greater magnitudes; however, these data must be interpreted with caution.

The understanding of the underlying mechanisms and causes of chronic diseases is transforming medicine from a reactive discipline to a proactive and preventive one. Therefore, a Predictive, Preventive, Personalized and Participatory Medicine (medicine P4) [40] which also applies to nutrition, with the objectives of quantifying well-being, will predict and prevent disease. Consumers are different in each country and the form of salt consumption is also different.

Tailoring treatment to each person’s characteristics means classifying others into subpopulations that differ in their susceptibility to a specific intervention or in their response to a specific treatment. Preventive interventions can then be focused on those who will benefit, saving resources for those who will not [41]. This approach reflects the importance of interventions that are based on the individual and not the general population.

The researchers identified three randomized studies with low-risk of bias that successfully reduced adults salt intake: dietary education and availability of a salt substitute with added potassium at village shops [28]; salt reduction in bread and nutritional advice [31]; and through the nutritional education of children who delivered the message to their families [27]. A reduction in salt intake is possible by integrating salt reduction education modules into school curricula and empowering children to deliver the message of salt reduction to their families. This intervention showed a new, viable and effective approach to reducing salt intake, and the authors showed an approximately 25% reduction in salt intake by the participants and a decrease in systolic blood pressure. Passing a salt reduction message to children has the potential to establish habits and attitudes that will persist throughout adult life, in addition to being able to reduce the consumption of salt by the family as well. It is an intervention that can be customized according to the children of each school. The authors report that to achieve a greater reduction in the population’s salt intake, this approach must be combined with other strategies such as working with the food industry to gradually reduce the amount of salt added to all processed foods [27].

The family also plays an important role in reducing salt intake in patients with heart failure [35], as family members can provide motivation and positive communication to change family habits [42].

Providing low-salt bread is an effective salt reduction strategy combined with nutritional counseling [26,30,31]. By reducing salt added to bread or other foods, the specific salt taste receptors in the mouth become much more sensitive to lower salt concentrations, meaning that less salty foods will stimulate a sensorial response similar to very salty foods before the adjustment [43]. This intervention can be one of the solutions for reducing salt in places where processed foods are one of the main sources of salt intake.

The use of salt substitutes with lower sodium content was a strategy used in interventions by three studies in this work [28,37,39]. Salt substitute is effective in reducing salt intake and has potassium in its constitution, increasing potassium intake by consumers. In the studies included in this work, potassium intake was higher in the intervention groups, but participants did not reach the WHO recommended daily intake (3510 mg/day). Also, a recent study showed that the use of salt substitute (with potassium in the constitution) decreased urinary sodium excretion and the rates of stroke, cardiovascular events, and deaths from any cause in people over 60 years of age [44].

The use of substitute salt costs about twice as much as regular salt [28], and it can be a social barrier in countries with less economic power. In addition, it has been reported that the taste of the salt substitute is bitter, not being accepted by all consumers [37]. It is important to consider whether dietary education focused on reducing salt intake can be a better and cheaper strategy that is more integrative from a social point of view. This work included seven interventions focused only on educating the individual to reduce salt intake and customized according to the target audience or their consumption habits. These interventions were successful and do not depend on the economic power of the consumer to buy a substitute that will make them ingest less salt.

In the study by Land et al. [39] the salt substitutes were part of a multifaceted community-based salt reduction program. As the intervention consisted of several components that were implemented simultaneously, it is not possible to quantify the relative contributions of each one to the success of the program. The same was found in the interventions by Anderson et al. [34] and Layeghiasl et al. [25], and it is not possible to identify a factor as being more important than another in the success of the intervention. Changing eating behavior is a complex process and dealing with multiple and interrelated factors appears to be effective in reducing salt intake [34]. The World Health Organization defends that different approaches can be applied in health education and communication campaigns; namely social mobilization, social marketing, behavior change communication and communication for development [12].

There is a growing trend towards self-monitoring of health, especially through apps such as calorie counters, exercise or dietary advice, and there is evidence that self-monitoring benefits users. Monitoring has the advantage that users can share dietary monitoring with healthcare professionals and receive immediate feedback or long-term follow-up [45]. It is a patient-centered and personalized service, making it possible to verify the individual’s salt intake and to be able to define strategies to reduce salt intake [36,46].

Maintaining the effects of salt-reducing interventions is difficult over time [47]. Sustainable changes in consumer behavior seem to be achievable through knowledge and awareness. Much of the population is not aware of the risks of salt consumption and its relationship with hypertension and its comorbidities. In addition to not being aware of the maximum recommended daily dose of salt intake, the amount of salt they eat and the main sources of salt in their diet [12].

The intervention based on the theory of planned behavior included in this work reduced salt intake by about 35% in the intervention group [24]. This approach is interesting in reducing salt consumption, as it customizes the intervention for each individual and there are different attitudes, stimulants and inhibitors about salt consumption in the population, in addition to several variables that affect the person’s control over behavior. However, a central factor in the theory of planned behavior is the individual’s intention to perform a certain behavior [48]. In the study by Rahimdel et al. [24] participants were at risk of developing hypertension, which can lead to being more motivated to change behavior than healthy individuals, which shows us that it is important to customize interventions according to the group target.

The researchers have also seen success in reducing salt intake in interventions based on nutrition education with a nutritionist [21,33], educating the consumer to read labels to select healthier foods that contain less salt [32] and cooking classes given by health professionals, including a nutritionist [19]. Having a health professional who can teach and raise awareness about the impact of salt consumption on health and the main sources of salt in the diet seems to help influence consumer behavior [12].

When searching for interventions that were successful in reducing salt intake, the researchers found 11 interventions that either had no statistically significant salt reduction or did not reduce salt intake.  These interventions included self-monitoring of salt excretion (n = 2) [49,50] and Na:K ratio (n = 1) [51] in urine. Self-monitoring of Na:K ratio excretion reduced salt excretion without statistical significance, probably because the sample size was insufficient and baseline potassium excretion was greater than the authors had expected. Also, in interventions with self-monitoring of salt excretion there was a non-statistically significant decrease in salt, the authors reported that this was probably due to a short intervention period (4 weeks) and insufficient sample size. Although these interventions were not included as successful interventions, it is likely that if they did not have problems with the methodology, they could have been successful. Participants being able to estimate salt intake appear to be effective salt reduction strategies as mentioned in other interventions [20,23] included in this work. A nutrition education intervention was unsuccessful in reducing salt, the intervention was to teach diabetic participants to use the nutrition information panel on food labels to choose products that comply with the Food Standards Australia New Zealand (FSANZ) guideline of <120 mg sodium/100 g food [52]. This intervention was used by Ireland et al. [38] in free-living adults and have successfully reduced salt. Therefore, this type of intervention is not effective in diabetics, which reinforces the importance of customizing interventions according to the population. We found three interventions that, in addition to nutrition education, used apps to reduce salt intake. Two interventions reduced salt without statistical significance and one intervention failed to reduce salt. Dorsch et al. [53] described an application-based intervention that sends just-in-time contextual adaptive messages. The reduction in urinary sodium excretion was 637 mg/day, but without statistical significance. Although the authors report that there were clinically significant improvements in the intervention group compared to the control, all participants were required to have an iPhone, so the effectiveness of this intervention may be related to the socioeconomic status of the participants. Lofthouse et al. [54] described an intervention that, in addition to using the app, used salt substitutes with lower sodium content, participants reduced salt excretion by 433 mg/day without statistical significance. This was a pilot study with only 11 volunteers, and these had a low baseline sodium (2342 mg) and so we probably could not see the potential of this intervention to reduce salt intake. In the study by Thatthong et al. [55] they described an intervention using a program that sends interactive messages about salt reduction. The study was carried out in hypertensive patients, at the end of the study, sodium excretion in the intervention group was higher than the baseline value. Although the sample size was small (n = 50), this result indicates that this intervention is probably not effective in reducing salt intake in hypertensive patients. Nakadate et al. [56] described an intervention in which they provided a salt monitoring instrument to measure the salt concentration of soup at home and low-sodium seasoning. They achieved a sodium reduction of 777 mg/day with monitoring and 413 mg/day with the low-sodium seasoning. Although the results were not statistically significant, probably due to the exploratory pilot design of the study, with sample size calculated based on provisional statistics, the results are interesting, especially the monitoring of salt in soup, in regions that have a high consumption of soup. Another study described an environmental and behavioral intervention in the workplace. They achieved an average reduction in salt intake of −0.6 g, from 8.7 g but without statistical significance. The authors reported that the cause of not achieving greater salt reduction was poor adherence to the study and programs in catering operations. The authors concluded that acceptance, effectiveness, and maintenance of workplace nutrition interventions require strong employer support [57]. Therefore, it is important to only consider intervening in the workplace when the employer is motivated to reduce the salt intake of workers. We found two studies that used Salt-Restriction-Spoon in the intervention. Chen et al. [58] in addition to the spoon, they provided nutritional education and informed the participants of the value of sodium excretion. At the end of the intervention, both the control group and the intervention group had decreased sodium excretion without statistical significance. Participants in both groups lived in the same place, probably causing contamination of the information for the study, the participants in the control group were informed about their sodium excretion, which may have contributed to the reduction in sodium excretion in this group. Cornélio et al. [59] described an intervention in hypertensive women that, in addition to the use of the Salt-Restriction-Spoon, provided an education based on behavior modification techniques to reduce salt intake. Also, in this intervention, both the control group and the intervention group decreased sodium excretion without statistical significance. Although the authors did not mention it is possible that there was an influence to reduce salt consumption in the control group because the women were asked to assess their usual monthly salt intake, and this may have led to awareness of the amount of salt they used and led them to reduce the amount they used when cooking. Salt-Restriction-Spoon are very interesting in populations where the biggest source of salt is the addition to cooking, helping people to limit the addition of salt.

Consumer education-based interventions alone reduce salt intake, but also when combined with other strategies. Tools for estimating salt consumption and self-monitoring of its consumption are also successful in reducing it.

Herein,  there is no evidence that the type of intervention analyzed is more effective in reducing salt consumption, but according to the medicine P4 approach, the researchers must analyze each revised intervention and verify in which individuals or subpopulations it is most beneficial and will lead to better results. However, the results must be interpreted with caution as the quality of the studies is mixed. In the future, it is important to develop more high-quality clinical trials, with a longer intervention time and more participants, in order to understand which interventions work best for the reduction of salt consumption according to the target population.