'Low-salt' Bread as a Means of Reducing Dietary Salt and Lowering Blood Pressure
Condition: Elevated Blood Pressure
MeSH terms: Hypertension
Study type: Interventional

Summary: 
      In the context of public health, reformulation of bread in terms of salt content remains an
      important measure to help achieve a reduction in salt intake in the population. Therefore,
      the aim of this study was to examine, using a 5-week cross-over design, food-based
      intervention trial, the potential for inclusion of 'low-salt' bread as part of a pragmatic
      reduced-salt diet on blood pressure (BP) in adults with slightly to moderately elevated BP.

      The study consisted of a randomized crossover trial of the effect of reduced-salt intake or
      usual-salt intake for 5 weeks on BP (as the primary outcome) in adults with slightly to
      moderately elevated BP (seated office systolic BP >120 and <160 mmHg or a diastolic BP >80
      and <95 mmHg; identified by a pre-screening phase).

      Subjects were randomly assigned to the reduced-salt diet or their usual-salt diet (control)
      for 5 weeks, followed by crossover to the alternative dietary regimen for a further 5 weeks.
      Subjects randomized to start on the reduced-salt diet were asked to restrict their
      consumption of dietary salt using a combination of pragmatic dietary advice as well as the
      replacement of bread and a limited number of other foods with equivalent foods which had
      lower salt content; these were provided to the participants. At the beginning of the salt
      restriction period, a research nutritionist provided the subjects with a list of the common
      salt-containing food and were asked to limit the consumption of such, as feasible. The
      subjects received in-house prepared 'low-salt (<0.3 g/100 g)' brown or white sliced pan bread
      as well as no-salt margarine/butter, and were given luncheon meats with no added salt, if
      desired (optional); these were supplied regularly by the research staff. Subjects commencing
      the trial on the control diet were allowed to follow their usual diet but were asked to
      consume an in-house produced brown or white sliced pan bread equivalent in composition to the
      low-salt version but with its more typical salt content (1.2 g/100 g).

      Participants met the research staff weekly to receive breads and no-salt margarine/butter as
      well as luncheon meats (where applicable), and at these meetings the staff promoted
      compliance with the intervention and encouraged completion of the study protocol.

      BP and other assessments were made at baseline and at the end of week 5 and week 10.
    

Detailed description: 
      Brief background and context for the study:

      The World Health Organization's Global Action Plan for the Prevention and Control of
      Non-Communicable Disease includes a voluntary global target of a 30% relative reduction in
      mean population intake of salt/sodium by 2025. Bread and cured/processed meats collectively
      contribute anything from about a third upwards of total salt intake of adults in many Western
      countries. Reformulation of bread in terms of salt content remains an important measure to
      help achieve a reduction in salt intake in the population. Therefore, the aim of this study
      was to examine, using a 5-week cross-over design, food-based intervention trial, the
      potential for inclusion of 'low-salt' bread as part of a pragmatic reduced-salt diet on blood
      pressure (BP) in adults with slightly to moderately elevated BP.

      Design:

      The study consisted of a randomized crossover trial of the effect of reduced-salt intake or
      usual-salt intake for 5 weeks on BP (primary outcome) and biochemical markers of calcium and
      bone metabolism as well as plasma lipids (secondary outcomes) in adults with slightly to
      moderately elevated BP.

      Potential volunteers were screened for BP over 3 weeks preceding the intervention phase of
      the trial during which seated office systolic and diastolic BP were measured weekly and those
      with systolic BP >120 and <160 mmHg or a diastolic BP >80 and <95 mmHg were considered
      eligible.

      The dietary intervention phase of the trial was designed in two successive dietary periods,
      each of 5 weeks. Subjects were randomly assigned to the reduced-salt diet or their usual-salt
      diet (control) for 5 weeks, followed by crossover to the alternative dietary regimen for a
      further 5 weeks. At baseline (week 0), the subjects visited the Human Nutrition Studies Unit
      within University College Cork in a fasting state and had their BP measured. Prior to the
      baseline visit, subjects received instructions on how to collect a 24-h urine sample and were
      provided with a suitable container for collection. On the day of the baseline visit, subjects
      brought the 24-h urine sample collected from the previous day and deposited it in a cold room
      area dedicated for such collections. A blood sample was taken from each subject between 08.30
      am and 10.30 am by a trained phlebotomist and anthropometric measures including height and
      weight, were taken. A health and lifestyle questionnaire, which assessed physical activity,
      general health, smoking status and alcohol consumption was completed by each subject.
      Subjects randomized to start on the reduced-salt diet were asked to restrict their
      consumption of dietary salt using a combination of pragmatic dietary advice as well as the
      replacement of bread and a limited number of other foods with equivalent foods which had
      lower salt content; these were provided to the participants. At the beginning of the salt
      restriction period, a research nutritionist provided the subjects with a list of the common
      salt-containing food and were asked to limit the consumption of such, as feasible. The
      subjects received in-house prepared 'low-salt (<0.3 g/100 g)' brown or white sliced pan bread
      as well as no-salt margarine/butter, and were given luncheon meats with no added salt, if
      desired (optional). Subjects commencing the trial on the control diet were allowed to follow
      their usual diet but were asked to consume an in-house produced brown or white sliced pan
      bread equivalent in composition to the low-salt version but with its more typical salt
      content (1.2 g/100 g).

      During the intervention phase, each participant made 2 further visits to the study unit, one
      each on the last day of dietary period 1 (week 5) and dietary period 2 (week 10). At these
      visits, BP measurements were taken as well as other anthropometric measures, including height
      and weight. An overnight fasting blood sample was also taken from each participant between
      08.30 am and 10.30 am by a trained phlebotomist, and on each of the visits, the subjects
      provided a 24-hour urine sample collected the previous day. Following blood sampling the
      participants received their breakfast.

      Participants met the research staff weekly to receive breads and no-salt margarine/butter as
      well as luncheon meats (where applicable), and at these meetings the staff promoted
      compliance with the intervention and encouraged completion of the study protocol.
    

Intervention name(s): Usual-salt diet; Reduced-salt diet
Intervention type(s): Other; Other
Intervention description(s): Subjects followed their usual-salt diet but were asked to consume an equivalent in-house produced brown or white sliced pan bread equivalent in composition to the low-salt version but with its more typical salt content (1.2 g/100 g).; Subjects randomized to start on the reduced-salt diet were asked to restrict their consumption of dietary salt using a combination of pragmatic dietary advice as well as the replacement of bread and a limited number of other foods with equivalent foods which had lower salt content; these were provided to the participants. At the beginning of the salt restriction period, a research nutritionist provided the subjects with a list of the common salt-containing food (salted and naturally salty) and were asked to limit the consumption of such, as feasible. The subjects received in-house prepared 'low-salt (<0.3 g/100 g)' brown or white sliced pan bread as well as no-salt margarine/butter, and were given luncheon meats with no added salt if desired (optional).
Allocation: Randomized
Intervention model: Crossover Assignment
Masking: Single (Outcomes Assessor)
Primary purpose: Prevention
Keywords: Low-salt bread; Dietary sodium restriction; Pre-hypertension; Hypertension stage 1