=Paper= {{Paper |id=Vol-1983/paper_01 |storemode=property |title=An Approach for Explaining Reasoning on the Diet Domain |pdfUrl=https://ceur-ws.org/Vol-1983/paper_01.pdf |volume=Vol-1983 |authors=Luca Anselma,Alessandro Mazzei |dblpUrl=https://dblp.org/rec/conf/aiia/AnselmaM17 }} ==An Approach for Explaining Reasoning on the Diet Domain== https://ceur-ws.org/Vol-1983/paper_01.pdf

An Approach for Explaining Reasoning on the
Diet Domain

Luca Anselma, Alessandro Mazzei

Dipartimento di Informatica, Università di Torino, Italy
{anselma,mazzei}@di.unito.it

Abstract. We are conducting a project involving automatic reasoning
and natural language generation in the domain of diet management. In
this paper we describe the main issues related to the automatic reasoning
mechanisms for diet management purposes and we present the message
generation techniques designed to support the users in managing their
dietary choices. In particular, this paper has two main goals. First, with
respect to the automatic reasoning module, we briefly describe the main
features of the Simple Temporal Problem formalization of the diet do-
main. Second, with respect to the natural language generation module,
we describe the actual implementation of the tasks of data interpretation
and content selection, and the design of the message templates; moreover,
we give a novel formalization of the sentence aggregation algorithm.

1 Introduction
People might fail to follow a healthy diet for a number of reasons. Sometimes
they do not know that a dish is in contrast to their diet or, in other cases, they
are not motivated enough since they do not have the right stimulus at the right
time. So, a diet management system needs to reason in order to enhance the
users’ computational abilities to recognize healthy dishes and needs to generate
a persuasive stimulus when it is really necessary, i.e., when the users have to
decide what to eat.
Similarly to [21] and [8] we want to investigate the possibility to apply au-
tomatic reasoning and persuasive NLG on mobile devices for helping people in
reaching a virtuous behaviour. In this paper we address some issues related to
numerical reasoning and persuasive natural language generation in the diet do-
main. We describe the actual implementation of the reasoning and generation
modules of the diet management system called MADiMan (Multimedia Applica-
tion for Diet Management) [5, 25]. In particular, after a brief description of the
numerical reasoner, which has been extensively described in [3, 6], we provide a
detailed description of the generation module.
The MADiMan system is a virtual dietitian (Fig. 1) designed: (1) to recover
the nutritional information directly from a specific recipe, (2) to reason over
recipes and diets by allowing some forms of diet disobedience, and (3) to per-
suade the user to minimize these acts of disobedience. MADiMan offers facilities

4
3. NLU/IE
Service

2. DietManager
1. APP Service
Recipe

4. Reasoner
Service

5. NLG
Service
DB users DB recipes

Fig. 1. The architecture of the diet management system.

to check the compatibility and to foresee the impact that a specific meal has on
a specific diet. In a diet it is necessary to consider parameters such as energy
requirements and the amount of macronutrients such as carbohydrates, lipids
and proteins. The medical literature (e.g., [23]) provides Dietary Reference Val-
ues (DRVs) that can be computed from user information such as weight, gender,
age, lifestyle. In MADiMan the reasoning module is a numerical reasoner based
on Simple Temporal Problems (STPs) where we represent the DRVs as STP
constraints [11] by substituting the temporal distance with the DRVs and the
caloric values of a dish distributed on the three macronutrients [6]. By using the
ideal value for calories, MADiMan evaluates the compatibility of the specific dish
with the actual status of the diet. Moreover, in order to provide a user-friendly
information not limited to “consistent/inconsistent” answer and to make it also
useful for the sake of user persuasion, MADiMan converts the numerical rea-
soning into a symbolic form that is suitable for the generation of NL messages
[31].
In the applicative scenario, the interaction between the man and the food is
mediated by an artificial intelligent system that encourages or discourages the
user to eat a meal that s/he intends to eat. The main factors that the system
needs to manage are: (1) the diet that the user intends to follow, (2) the food that
has been eaten in the last days, and (3) the specific recipes of the dishes and
the nutritional values of their ingredients. The complete MADiMan system is
composed of five modules (see Fig. 1): a smartphone application (app), a central

5
module that manages the information flow (DietManager), a Natural Language
Understanding / Information Extraction (NLU/IE) module, a reasoning module
(Reasoner), a natural language generator module (NLGenerator). Upon a regis-
tration where the user provides her anthropometric data, the information flow
follows this pattern:

1. The user, by using the app, recovers the QR-code of a specific recipe, or
finds the recipe using full-text search.
2. The app, using the DietManager service, retrieves the user diet together with
the list of the food that the user has eaten in the last days. Moreover, the
DietManager retrieves the specific recipe of the specific dish.
3. The NLU/IE module computes the salient nutrition information about the
specific dish.
4. The Reasoner, using the user diet and the list of the food that has been
eaten in the last days, produces a judgment about the dish for the user.
5. The NLGenerator uses the result given by the Reasoner, produces an expla-
nation for the user in plain natural language and/or in a multimedial format
(e.g. by using icons).
6. The DietManager sends the result produced by the NLGenerator to the app:
the user will see this final result on her smartphone. If the user decides to
eat the dish, the app will send this information to the DietManager that will
update the list of food eaten. So, the DietManager plays the role of a hub.

We think that this system could be commercially attractive at least in two
contexts. The first context is the medical one, where users (e.g. patients affected
by essential obesity) are strongly motivated to strictly follow a diet and need tools
that help them. The second context is the one involving, e.g., healthy fast food
or restaurant chains, where the effort of deploying the system can be rewarded
by an increase in customer retention. However, for a complete implementation,
in the diet management architecture depicted in Figure 1 there are a number of
choices which need to be experimentally evaluated. For instance, there are many
technologies available on smartphones, such as the GPS localization or speech
recognition, that could be used for the insertion of the data. All these choices
are important to create a highly usable system supporting and motivating users
in their daily life [24].
In this paper1 , we first briefly describe the STP reasoner in Section 2, and sec-
ond we give some details concerning the NLG module in Section 3. In particular
we describe current implementation of three specific modules of the generator:
in Section 3.1, we describe the data interpretation and content selection process
for converting the numerical output of the STP reasoner into a symbolic form.
In Section 3.2, we describe the design of five templates for the realization of the
persuasive messages for the three macronutrients, and in Section 3.3 we provide
a novel formalization of the algorithm used to aggregate the messages. Finally,
Section 4 closes the paper with some conclusions and pointers to future work.
1
Some details on the app, the DietManager service, the NLU/IE service can be found
on the webpage of the project MADiMan: http://di.unito.it/madiman.

6
2 Automatically reasoning on diets
In this section first we introduce “Simple Temporal Problem” (STP), and then we
describe how we exploit STP for representing reasoning over dietary information.
In contrast to other approaches to diet formalization, for example [15]2 which is
based on ontologies, we approach the diet management problem from a numerical
perspective since STP is a numerical constraint satisfaction formalism.

2.1 Simple Temporal Problems
An STP constraint [11] is a bound on differences of the form c ≤ x−y ≤ d, where
x and y are temporal points and c and d are numbers whose domain can be either
discrete or real. An STP constraint can be interpreted in the following way: the
temporal distance between the temporal points x and y must be between c –
the lower bound of the distance – and d – the upper bound. It is also possible
to impose strict inequalities (i.e., <) and to use −∞ and +∞ to denote the fact
that there is no lower or upper bound, respectively. An STP is a conjunction of
STP constraints.
STP can be represented as a graph whose nodes are the temporal points and
the arcs are labeled with the temporal distance between the points.
A prominent feature of STP is that the problem of determining the con-
sistency of an STP is tractable and the algorithm employed, i.e., an all-pairs
shortest paths algorithm such as Floyd-Warshall’s one, also obtains the mini-
mal network. A minimal network is equivalent to the original STP and it makes
explicit all the implied STP constraints by representing the strictest constraint
between each pair of point, which corresponds to the minimum and maximum
distance between each pair of points. Floyd-Warshall’s algorithm is correct and
complete on STP, i.e. it performs all and only the correct inferences while prop-
agating the STP constraints [11]. Its temporal computational cost is cubic in the
number of the temporal points.

2.2 Reasoning on the energy requirements and energy intake
It has been proven that excessive calorie intake – and subsequent obesity –
increases the risk of developing chronic disease and decreases life expectancy [17].
In order to restrict calorie intake, one of the most important feature to be taken
into account in a diet is the total energy requirement. In particular, from a user’s
weight, gender and age, using Schofield equation [34], it is possible to estimate
her basal metabolic rate as reported in Table 1. For example a 40-year-old male
who weighs 71.3 kg has an estimated basal metabolic rate of 1690 kcal/day.
Such value is then adjusted by multiplying the basal metabolic rate by a factor
related with the physical activity of the individual; for example, if the person
has a sedentary lifestyle, a factor of 1.45 is employed so that he has a total
energy requirement of 1690 · 1.45 = 2450 kcal/day. It is worth noting that our
2
We thank an anonymous reviewer for pointing us to this work.

7
system does not depend on the particular formula used to compute the total
energy requirement, and it is possible to employ other formulas or the dietitian
can even empirically estimate the value for specific patients.
Using STP constraints it is possible to represent the total energy require-
ment and also the dietary prescription regarding the meals’ calorie amounts. For
instance, the daily energy requirement of 2450 kcal/day is represented by the
STP constraint dayE − dayS = 2450 and the recommendation to eat a lunch of
minimum 500 kcal and maximum 600 kcal is represented by the STP constraint
500 ≤ lunchE − lunchS ≤ 600, where dayE , dayS , lunchE and lunchS represent
the end and the start of the day and of the lunch, respectively.

2.3 Supporting dietary transgressions

We exploit the STP framework to allow users to make small deviations from the
ideal goal of sticking to their energy requirements and to know in advance what
are the consequences of such deviations on the rest of the diet.
Thus, we admit a tolerance in adhering to the diet constraints. Such a
tolerance generates loose constraints over the shortest periods (i.e., days and
meals) and strict constraints over the longest periods (i.e., weeks), thus al-
lowing episodes of transgression in the short term that however do not pre-
vent a user from reaching the diet goal. Let σw , σd and σm be the toler-
ances for the week, the days and the meals respectively, σw ≤ σd ≤ σm .
For example the recommended energy requirement of 2450 kcal/day, consid-
ered over a week and considering a tolerance σw , results in a constraint such
as 2450 · 7 · (1 − σw ) ≤ weekE − weekS ≤ 2450 · 7 · (1 + σw ) and for the
single days we allow the user to have a tolerance σd , thus resulting in the
constraints 2450 · (1 − σd ) ≤ SundayE − SundayS ≤ 2450 · (1 + σd ), . . . ,
2450 · (1 − σd ) ≤ SaturdayE − SaturdayS ≤ 2450 · (1 + σd ) (see Fig. 2a).
For single meals we consider that the energy assumption for the day is split
among the meals; for example, assigning 20% for breakfast, 40% for lunch and
40% for dinner, and that we allow a tolerance of σm , we obtain constraints
such as 2450 · 20% · (1 − σm ) ≤ Sunday breakf astE − Sunday breakf astS ≤
2450·20%·(1+σm ) and 2450·20%·(1−σm ) ≤ Sunday lunchE −Sunday lunchS ≤
2450 · 20% · (1 + σm ).

Age (years) Basal metabolic rate (kcal/day)
Men
18 − 29 ((0.063 · weight) + 2.896) · 238.8459
30 − 59 ((0.048 · weight) + 3.653) · 238.8459
> 60 ((0.049 · weight) + 2.459) · 238.8459
Women
18 − 29 ((0.062 · weight) + 2.036) · 238.8459
30 − 59 ((0.034 · weight) + 3.538) · 238.8459
> 60 ((0.038 · weight) + 2.755) · 238.8459

Table 1. Schofield equation for estimating the basal metabolic rate [34].

8
2450∙7
a)

[2205,2695] [2205,2695] [2205,2695] [2205,2695] [2205,2695] [2205,2695] [2205,2695]
0 0 0 0 0 0
Sun Mon Tues Weds Thurs Fri Sat

2270∙4
b)

2690 2690 2690 [2205,2465] [2205,2465] [2205,2465] [2205,2465]
0 0 0 0 0 0
Sun Mon Tues Weds Thurs Fri Sat

Fig. 2. a) Example of STP constraints for a week (with σw = 0 and σd = 10%). For
space constraints the constraints for the meals are not represented. b) Example of
STP constraints after three day when the user has eaten 2690 kcal and the constraint
propagation has been performed.

In order to build a sound STP, it is also necessary to add STP constraints
such the ones that impose that a day ends when the subsequent day starts (see,
for example, the constraints 0 in Fig. 2a), that a week starts when the first day
of the week starts, that a week ends when the last day of the week ends and the
analogous constraints for the meals.
A compatible meal is a meal that satisfies all the STP constraints that involve
such a meal.

2.4 Representing and reasoning on the diet and the food
We wish to support users into taking advantage of the information regarding
the actual meals they consume. In this way, such users can apprehend what
are the consequences on their diet of eating a specific meal and they could
use such information to make informed decisions about their current or future
meals. Therefore it is necessary to “integrate” the information about the eaten
meals with the dietary recommendations. Thus, as the users eat their meals, we
substitute in the STP the original STP constraint related with the diet with the
information regarding the actual energetic supply of such meals.
For example, let us suppose that a user on Sunday, Monday and Tuesday had
an actual intake of 2690 kcal for each day. This corresponds to adding to the STP
the new constraints SundayE − SundayS = 2690, . . . , T uesdayE − T uesdayS =
2690. Then, propagating the constraints of the new STP, we discover (see Fig. 2b)
that (i) the STP is consistent and thus the intake is compatible with the diet
and (ii) on each remaining day of the week the user has to assume a minimum
of 2205 kcal and a maximum of 2465 kcal.

9
3 Persuasive NLG for diet
A widespread architecture for NL generation, especially in applicative contexts,
is a pipeline composed by three distinct modules: the document planning, the
sentence planning and the surface realization [32]. Each one of these modules
addresses distinct issues, in particular: (1) in the document planning one decides
what to say, i.e., which information contents will be communicated; (2) in the
sentence planning, the focus is on the design of a number of features that are
related to the information contents as well as to the specific language, as the
choice of the words; (3) in the surface realization, sentences are finally generated
on the base of the decision taken by the previous modules and by considering
the constraints related to the language-specific word order and inflections.
For our system, the contents of information that have to be communicated,
i.e. the document planning, are produced by the STP reasoner, and we need
to convert such contents into a human-readable form: we address this issue in
the Section 3.1. Moreover, with the aim to easily implement in the messages the
prescriptions of the persuasion theories, we adopted the simplest architecture for
NLG. Similar to other works, e.g. [15], we treat sentence planning and surface
realization in one single module by adopting a template-based approach. We
describe the templates in the Section 3.2. Finally, in Section 3.3 we formalize
the sentence aggregation algorithm used to merge messages concerning distinct
macronutrients.

3.1 Data interpretation and content selection
In order to show to the user a meaningful feedback, it is necessary to interpret
the data resulting from the STP. Here we consider the case where the user
proposes to the system a dish, the system obtains its caloric value, translates
it along with the user’s diet and past meals into an STP and, by propagating
the constraints, obtains the minimal network. For sake of clarity, we present the
content selection algorithm by considering one single generic macronutrient, but
the real suitability of a dish depends on the results of the three macronutrients
(see Section 3.3).
Using the resulting STP it is possible to classify the proposed dish in one of
the following five cases: permanently inconsistent (I1 ), occasionally inconsistent
(I2 ), consistent and not balanced (C1 ), consistent and well-balanced (C1 ) and
consistent and perfectly balanced (C3 ). In the cases I1 and I2 the energy supply of
the dish is inconsistent. In case I1 the energy supply is inconsistent with regard
to the user’s diet as represented in the STP considering the tolerance values.
The dish cannot be accepted even independently of the other food the user may
possibly eat. This case is detected by considering whether the nutritional value
of the dish violates a constraint in the STP. In case I2 the dish per se does not
violate the diet constraints, but – considering the past meals the user has eaten
– it would preclude to be consistent with the diet. Thus, it is inconsistent now,
but in the future, e.g., next week, it could become possible to choose it. This
case is detected by determining whether the energy supply, despite it satisfies

10
I1hyper
inconsistent
I2hyper
max
not balanced C1hyper

hyper t2
well
C2hyper
balanced
t1
perfectly C3
balanced ???
Ideal value
perfectly
C3
balanced
t1
well
C2hypo
balanced
hypo t2

not balanced C1hypo
min
I2hypo
inconsistent
Calories I1hypo

Fig. 3. Classification of an inconsistent/consistent value of a meal’s energy supply given
the minimum and maximum value of an STP constraint.

the constraints in the initial STP, is inconsistent with the STP that contains
also the constraints related to the food that the user has actually eaten so far.
In the cases C1 , C2 and C3 the value of the energy supply is consistent with
the diet, also taking into account the other meals that the user has already
eaten. It is possible to detect that a meal is consistent by exploiting the minimal
network of the STP: if the value of the energy supply is included between the
lower and upper bounds of the relative STP constraint, then the STP is certainly
consistent and the meal is consistent with the diet. A consistent but not balanced
choice of a meal will have consequences on the rest of the user’s diet because the
user will have to “compensate” it. Thus we distinguish three cases depending
on the level of the adequacy to the diet of the meal’s energy supply. In order
to discriminate between the cases C1 , C2 and C3 , we consider how the value of
the energy supply stacks upon the allowed range represented in the related STP
constraint. We assume that the mean value is the “ideal” value according to the
diet’s goals and we consider two parametric user-adjustable thresholds relative
to the mean: we classify the meal according to the distance from the ideal value
as not balanced (C1 ), well balanced (C2 ) or perfectly balanced (C2 ) (see Fig. 3).
In particular, we distinguish between excess or lack of energy supply for a meal:
if a meal is in excess (lacking) with regard to the ideal value, we tag the meal
with the keyword hyper (hypo). This information is exploited in the generation
of the messages.

11
3.2 Designing five templates for realizing persuasive messages

In order to convert in sentences the five possible kinds of output of the STP
reasoner, at this stage of the project we adopted a simple template-based real-
izer that produces five kinds of messages designed for persuasion. We use five
templates to communicate the five cases of output of the reasoner, that are I1 ,
I2 , C1 , C2 and C3 . For sake of clarity, we describe the templates by assuming
one single macronutrient. In the Section 3.3 we discuss how to aggregate the
three messages generated for the three distinct macronutrients.
In the NLG community there are a few works treating the generation of
persuasive messages the diet domain, e.g. [27, 15]. Moreover, a larger number
of works considering the application of NLG for presenting the results of auto-
mated reasoning to the user, especially in the case of expert systems, e.g. [36, 7,
22]. Moreover, a number of theories on the design of persuasive textual and mul-
timedial messages have been proposed in the last years. Most of these theories
can be split in two narrow categories. The first category includes the theories
that approach the persuasion from a practical and empirical point of view, by
using strategies and methods typical of the psychology and of the interaction
design [16, 30, 9, 21]. The second category includes the theories that approach
the persuasion from a theoretical point of view, by using strategies and methods
typical of strong artificial intelligence and cognitive science [20, 33, 19].
As a working hypothesis, the actual implementation of the generator pro-
duces messages following a fixed rhetorical schema. So, the final message will be
composed by three parts: a global evaluation of the dish, three evaluations for
the macronutrients (i.e. carbohydrates, lipids, proteins), and a suggestion on the
future dishes to eat.
In Table 2, we report the five cases obtained by the interpretation of the
output of the reasoner and the direction of the deviation (column O), and the
template3 (column Message Template). Indeed, the final message is obtained
by modifying the templates on the basis of the specific values for the motivation
of inconsistency that can be extracted by interpreting the output of the reasoner
(cf. Section 3.1) and some possible suggestions that can guide the choices of the
user in the next days. The suggestions can be obtained by querying a database
in order to couple the excess (deficiency) of a macronutrient with a dish that can
compensate this excess (deficiency). In particular, for the reasoner’s outputs I1 ,
I2 , C1 and C2 , we need to distinguish the case of a dish low in a macronutrient
(hypo in Table 2) with respect to the case of a dish high in a macronutrient
(hyper ). If the dish is classified as hypo (hyper ), we insert into the message
a suggestion to consume in the next days a dish with an increased (reduced)
amount of that macronutrient.

Adopting persuasion theories in the templates
3
For space reasons, we report here the English version of the message and we omit
the original Italian version.

12
O Message Template
I1hypo This dish is not good at all, it’s too poor in proteins!
You cannot have this dish now because it doesn’t provide enough proteins,
I2hypo but if you eat a nice dish of beans Sunday, you can have it on
Monday.
This dish is good, but it’s poor in proteins. In the next days
C1hypo
you’ll have to eat really more proteins.
This dish is OK, but it’s a bit poor in proteins. In the next days you’ll
C2hypo
need more proteins! :)
C3 Great choice! This dish is perfect for the proteins in your diet :)

Table 2. The persuasive message templates for the STP modeling caloric value for the
proteins. The underlined text vary among the three macronutrients.

Similar to [21], the Cialdini’s general theory of persuasion has inspired our de-
sign of the messages [9]. Cialdini states that there are six patterns which are
characteristic of human nature: (1) Reciprocity: people feel obligated to return a
favor, (2) Scarcity: people will value scarce products, (3) Authority: people value
the opinion of experts, (4) Consistency: people do as they said they would, (5)
Consensus: people do as other people do, (6) Liking: we say yes to people we like.
Note that compared to the six Cialdini’s persuasion patterns, all the messages
in Table 2 belong to the patterns of authority and consistency.
With respect to the low-level linguistic strategies, by following [33], we used
a number of adverbs (little bit, very, really) in order to enhance or mitigate a
message for the cases I1 , I2 , C1 and C2 . Furthermore, compared to Guerini et
al. persuasive strategies taxonomy [19], we can see that all the messages be-
long to one single category, called action-inducement & goal-balance & positive-
consequence. This strategy induces an action (i.e. to choose a dish), by using the
user’s goal (i.e. a healthy diet) and by using the benefits deriving from this goal.
Finally, note that in the messages C2 and C3 we used emoticons. Indeed, some
studies have showed that the use of emoticons in written texts can increase the
communicative strength of a specific class of messages. In particular, Dirke has
showed that the use of emoticons sets a tone of friendship to the communication
and can increase the positive value of the message [12].

3.3 Modelling aggregation for messages on macronutrients
The aggregation plays an important role to generate fluent and efficient texts
[13]. In the previous section we presented a template-based approach for the
generation of a message concerning one single macronutrient. In this section we
introduce an algorithm for aggregating the three messages for the three macronu-
trients. We write (OC , OL , OP ) to indicate the symbolic output for carbohy-
drates, lipids and proteins respectively, where

OX ∈ {I1hypo , I1hyper , I2hypo , I2hyper C1hypo , C1hyper , C2hyper , C2hypo , C3 }

13
Indeed, a trivial aggregation strategy could merge only messages that belong to
the same category, i.e. Ox =Oy : this simple strategy corresponds to the syntac-
tic aggregation in the classification of [29]. However, we design an aggregation
strategy that accounts for a more sophisticated form of conceptual aggregation.
The general idea of the aggregation algorithm is to merge messages that are in
same category giving more emphasis to the incompatibility messages. So, there
are three alternative cases:

A. ∃X ∈ {C, L, P } : OX =I1hypo ∨ OX =I1hyper
B. ∀X ∈ {C, L, P } : (OX 6= I1hypo ∧ OX 6= I1hyper ) ∧ ∃Y ∈ {C, L, P } : (OY =
I2hypo ∨ OY =I2hyper )
C. otherwise, i.e. ∀X ∈ {C, L, P } ∃i ∈ {1, 2, 3} : (OX =Cihypo ∨ OX =Cihyper )

In the case A. there is at least a permanent inconsistency for a macronutrient,
in the case B. there is no permanent inconsistencies but at least an occasional
inconsistency, and in the case C. all the macronutrients are consistent.
In the cases A. and B., we aggregate the messages by exploiting the infor-
mation about incompatibility, that is (i) by merging the messages about incom-
patible macronutrients, (ii) by removing the messages concerning the compatible
macronutrients; moreover, for the case B., (iii) we give a suggestion for the fu-
ture meals. For instance, suppose that the symbolic interpretation of the STP
gives (OC =I1hypo , OL=I1hypo , OP =C1hyper ), the final message will be:
You cannot eat this dish because it’s too poor in carbohydrates and lipids!
while in the case of (OC =I2hypo , OL =C2hypo , OP =I2hypo ), the final message will
be:
You cannot have this dish now because it doesn’t provide enough carbohy-
drates and proteins, but if you eat a nice dish of pasta and beans on Sunday,
you can have it on Monday.
In the case C., that is when the macronutrients are all compatible, we define
10 distinct aggregation patterns (cf. [10]) by considering the possible occurrences
of the values C1 , C2 and C3 in (OC , OL , OP ) disregarding the order (i.e. the
specific macronutrient).
In this case the algorithm first aggregates messages belonging to categories C1
and C2 , and second orders the aggregated messages. The order of the aggregated
messages follows their compatibility value: the idea is to start with the most
positive feedback, as suggested by some theories of persuasion [35, 14]. Formally,
the patterns aggregate two messages Ox =Ci and Oy =Cj if i, j∈{1, 2}, and the
message Ox=Ci will be communicated earlier of Oy =Cj if i>j. For instance, in
the case of (OC =C1hypo , OL=C2hypo , OP =C3 ), the aggregated message will be:
This dish is good. It is perfect for the proteins, but it is a bit poor in lipids
and really poor in carbohydrates,
while in the case of (OC =C3 , OL=C2hyper , OP =C3 ), the aggregated message will
be:
This dish is good. It is perfect for the proteins and the carbohydrates, but
it is a bit too rich in lipids.

14
4 Conclusions and future work
In this paper we have described an approach for diet management based on auto-
matic numerical reasoning and natural language generation. We have introduced
the main features of an STP-based reasoning for the diet domain. Moreover, we
have illustrated the design of the NL generation of persuasive messages in the
diet domain, i.e. content selection, linguistic design of templates and aggregation
algorithm.
As a future work, in order to augment the variety of the messages, we intend
to replace the template-based realizer with a realization engine [18, 26].
We have some experience on working on patient data and collaborating with
hospitals [28, 2, 1, 4] and we envision a collaboration with hospital dietitians to
evaluate the system by comparing the persuasive NLG output with graphical
output representing the numerical values of the macronutrients. We are currently
working on the implementation of a mobile app and on its exploitation in a
human evaluation of MADiMan, performed by nutrition and dietistics students
which will be supervised by some professional dietitians.

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